Sommaire - Triangle de la Physique
Transcription
Sommaire - Triangle de la Physique
PUBLICATIONS PROJETS 2008 Sommaire [2008-002T] EEES .................................................................................................................................................. 7 Excited electron dynamics in Cu nanowires supported on a Cu(111) surface .................................................... 7 Extraordinary Electron Propagation Length in a Metallic Double Chain Supported on a Metal Surface ........... 7 Mapping of the electron transmission through the wall of a quantum corral ...................................................... 7 [2008-005T] EXTREME ........................................................................................................................................ 8 A microscopic view on the Mott transition in chromium-doped V2O3 .............................................................. 8 [2008-007T] QCCM ............................................................................................................................................... 9 Binary and ternary recombination of D-3(+) ions with electrons in He-D-2 plasma .......................................... 9 Binary and ternary recombination of H-3(+) and D-3(+) ions with electrons in low temperature plasma.......... 9 Calculation of rate constants for vibrational and rotational excitation of the H+(3) ion by electron impact .... 10 Optical phase and the ionization-dissociation dynamics of excited H2 ............................................................ 10 Assignment of resonances in dissociative recombination of HD(+) ions: High-resolution measurements compared with accurate computations .............................................................................................................. 10 Electron collisions with BF+: bound and continuum states of BF .................................................................... 11 Formation of the simplest stable negative molecular ion H3- in interstellar medium ....................................... 11 Laser control of complete vibrational transfer in Na2 using resonance coalescence ........................................ 11 Laser cooling of the vibrational motion of Na(2) combining the effects of zero-width resonances and exceptional points ............................................................................................................................................. 12 Photoassociation of a cold-atom-molecule pair. II. Second-order perturbation approach ................................ 12 Proposal for a Laser Control of Vibrational Cooling in Na-2 Using Resonance Coalescence .......................... 12 Triplet-singlet conversion in ultracold Cs-2 and production of ground-state molecules ................................... 13 Breaking a tetrahedral molecular ion with electrons: study of NH4+ ............................................................... 13 Potential energy and dipole moment surfaces of HCO- for the search of H- in the interstellar medium .......... 13 Photoassociation of a cold-atom-molecule pair: Long-range quadrupole-quadrupole interactions .................. 14 Cold atom-molecule photoassociation: long-range interactions beyond the 1/Rn expansion ........................... 14 Laser cooling of the vibrational motion of Na2 combining the effects of Zero Width Resonances and Exceptional Points. ............................................................................................................................................ 14 Long-range interactions between ultracold atoms and molecules including atomic spin-orbit ......................... 15 Photoassociation of a cold atom-molecule pair II: second-order perturbation approach .................................. 15 Potential energy and dipole moment surfaces of HCO- for the search of H- in the interstellar medium .......... 15 Theory of dissociative recombination of a linear triatomic ion with permanent electric dipole moment: Study of HCO+............................................................................................................................................................ 16 [2008-015T] ULYSSE & [2009-004T] ULYSSE II ............................................................................................. 16 Insight into low frequency noise induced by gate leakage current in AlGaAs/GaAs high electron mobility transistors at 4.2 K ............................................................................................................................................ 16 Input Noise Voltage Below 1 nV/Hz(1/2) at 1 kHz in the HEMTs at 4.2 K ..................................................... 16 The Role of the Gate Geometry for Cryogenic HEMTs: Towards an Input Voltage Noise Below 0.5 nV/root Hz at 1 kHz and 4.2 K ....................................................................................................................................... 17 28/02/2013 1 PUBLICATIONS PROJETS 2008 [2008-016T] SMGM ............................................................................................................................................. 17 Elementary excitation modes in a granular glass above jamming ..................................................................... 17 [2008-019T] MCQM............................................................................................................................................. 18 Multiple-measurement Leggett-Garg inequalities ............................................................................................. 18 Implementation of a Nondeterministic Optical Noiseless Amplifier ................................................................ 18 Nondeterministic noiseless amplification of optical signals: a review of recent experiments .......................... 18 [2008-020T] MICROHALL.................................................................................................................................. 19 A local noise measurement device for magnetic physical systems ................................................................... 19 [2008-025T] FLUCT-DMABN............................................................................................................................. 19 Do fluorescence and transient absorption probe the same intramolecular charge transfer state of 4(dimethylamino)benzonitrile? ........................................................................................................................... 19 Intramolecular charge transfer and dual fluorescence of 4-(dimethylamino) benzonitrile: ultrafast branching followed by a two-fold decay mechanism ......................................................................................................... 19 [2008-026T] Prodymag ......................................................................................................................................... 20 Dynamic fluctuations and two-dimensional melting at the spin reorientation transition .................................. 20 [2008-027T] POMICO .......................................................................................................................................... 20 Organization of Block Copolymers using NanoImprint Lithography: Comparison of Theory and Experiments .......................................................................................................................................................................... 20 Tailoring Nanostructures Using Copolymer Nanoimprint Lithography ........................................................... 21 Block Copolymer at Nano-Patterned Surfaces .................................................................................................. 21 [2008-028T] MASLOV ........................................................................................................................................ 21 Nonanalytic Spin Susceptibility of a Fermi Liquid: The Case of Fe-Based Pnictides ...................................... 21 [2008-029T] HY-IRGS-2 ...................................................................................................................................... 22 Emergence of Rigidity at the Structural Glass Transition: A First-Principles Computation ............................. 22 Replica theory of the rigidity of structural glasses ............................................................................................ 22 [2008-031T] STOLTE .......................................................................................................................................... 23 Unusual Quantum Interference in the S-1 State of DABCO and Observation of Intramolecular Vibrational Redistribution .................................................................................................................................................... 23 [2008-032T] B-DIAMANT .................................................................................................................................. 23 Influence of a static magnetic field on the photoluminescence of an ensemble of nitrogen-vacancy color centers in a diamond single-crystal ................................................................................................................... 23 Avoiding power broadening in optically detected magnetic resonance of single NV defects for enhanced dc magnetic field sensitivity .................................................................................................................................. 24 [2008-046T] DYNELEC ....................................................................................................................................... 24 Ion Pair Formation in Multiphoton Excitation of NO2 Using Linearly and Circularly Polarized Femtosecond Light Pulses: Kinetic Energy Distribution and Fragment Recoil Anisotropy ................................................... 24 Molecular frame photoemission in dissociative ionization of H-2 and D-2 induced by high harmonic generation femtosecond XUV pulses ................................................................................................................ 25 [2008-047T] GAIN ............................................................................................................................................... 25 Enhanced photoluminescence of heavily n-doped germanium ......................................................................... 25 28/02/2013 2 PUBLICATIONS PROJETS 2008 Band structure and optical gain of tensile-strained germanium based on a 30 band k center dot p formalism . 26 Control of direct band gap emission of bulk germanium by mechanical tensile strain ..................................... 26 Direct and indirect band gap room temperature electroluminescence of Ge diodes ......................................... 26 Control of tensile strain in germanium waveguides through silicon nitride layers ........................................... 27 [2008-048T] SPECTMAG .................................................................................................................................... 27 Atomic structure of tip apex for spin-polarized scanning tunneling microscopy .............................................. 27 [2008-051T] PHOTO-MAG ................................................................................................................................. 28 Controlled growth of core@shell heterostructures based on Prussian blue analogues...................................... 28 Magnetic Core-Shell Nanoparticles from Nanoscale-Induced Phase Segregation ............................................ 28 Influence of Protected Annealing on the Magnetic Properties of gamma-Fe2O3 Nanoparticles ...................... 29 [2008-052T] ACOUSTIC ..................................................................................................................................... 29 Homogeneous broadening of the S to P transition in InGaAs/GaAs quantum dots measured by infrared absorption imaging with nanoscale resolution .................................................................................................. 29 [2008-053T] SERPBIO ......................................................................................................................................... 30 First observation in the gas phase of the ultrafast electronic relaxation pathways of the S-2 states of heme and hemin................................................................................................................................................................. 30 Strength of (NHS)-S-Hydrogen Bonds in Methionine Residues Revealed by Gas-Phase IR/UV Spectroscopy .......................................................................................................................................................................... 30 [2008-053T] SERPEBIO & [2010-003T] COMOVA .......................................................................................... 31 Unraveling the Mechanisms of Nonradiative Deactivation in Model Peptides Following Photoexcitation of a Phenylalanine Residue ...................................................................................................................................... 31 [2008-054T] SYMTCOB ...................................................................................................................................... 31 Growth and characterisation of Li(x)CoO(2) single crystals ............................................................................ 31 Na-23 NMR study of sodium order in NaxCoO2 with 22 K Neel temperature ................................................ 32 [2008-055T] GRAMINE ....................................................................................................................................... 32 Conductive-probe AFM characterization of graphene sheets bonded to gold surfaces..................................... 32 [2008-056T] FLAG ............................................................................................................................................... 33 Anatomy of a femtosecond laser processed silica waveguide [Invited] ............................................................ 33 Dependence of the femtosecond laser refractive index change thresholds on the chemical composition of doped-silica glasses ........................................................................................................................................... 33 Modification thresholds in femtosecond laser processing of pure silica: review of dependencies on laser parameters [Invited] .......................................................................................................................................... 33 Time-resolved plasma measurements in Ge-doped silica exposed to infrared femtosecond laser .................... 34 Gold Nanoparticles Reshaped by Ultrafast Laser Irradiation Inside a Silica-Based Glass, Studied Through Optical Properties .............................................................................................................................................. 34 Oriented creation of anisotropic defects by IR femtosecond laser scanning in silica ....................................... 34 Three-dimensional photoprecipitation of oriented LiNbO3-like crystals in silica-based glass with femtosecond laser irradiation ................................................................................................................................................. 35 [2008-057T] PAO ................................................................................................................................................. 35 Dielectric gratings for wide-angle, broadband absorption by thin film photovoltaic cells................................ 35 28/02/2013 3 PUBLICATIONS PROJETS 2008 Optical Patch Antennas for Single Photon Emission Using Surface Plasmon Resonances .............................. 35 Experimental study of hot spots in gold/glass nanocomposite films by photoemission electron microscopy .. 36 Nanoscale magnetic field mapping with a single spin scanning probe magnetometer...................................... 36 [2008-058T] FemtoARPES ................................................................................................................................... 36 Coherent Phonon Coupling to Individual Bloch States in Photoexcited Bismuth ............................................ 36 Giant Anisotropy of Spin-Orbit Splitting at the Bismuth Surface ..................................................................... 37 Ultrafast Surface Carrier Dynamics in the Topological Insulator Bi2Te3 ........................................................ 37 Ultrafast filling of an electronic pseudogap in an incommensurate crystal ....................................................... 38 [2008-060T] MeMoFri .......................................................................................................................................... 38 Contact Angle and Contact Angle Hysteresis Measurements Using the Capillary Bridge Technique ............. 38 Incidence of the molecular organization on friction at soft polymer interfaces ................................................ 38 Synthesis of well-defined poly(dimethylsiloxane) telechelics having nitrobenzoxadiazole fluorescent chainends via thiol-ene coupling ............................................................................................................................... 39 Wetting and Dewetting Transition: An Efficient Toolbox for Characterizing Low-Energy Surfaces .............. 39 [2008-061T] MINIATOM .................................................................................................................................... 40 Light-pulse atom interferometry in microgravity .............................................................................................. 40 Frequency doubled 1534nm laser system for potassium laser cooling ............................................................. 40 [2008-062T] DYNANEX...................................................................................................................................... 40 Photoionization of 2-pyridone and 2-hydroxypyridine ..................................................................................... 40 A two-step ICT process for solvatochromic betaine pyridinium revealed by ultrafast spectroscopy, multivariate curve resolution, and TDDFT calculations ................................................................................... 41 Femtosecond dynamics of cyclopropenylidene, c-C3H2 .................................................................................. 41 [2008-063T] SAMNANO ..................................................................................................................................... 42 UPS, XPS, and NEXAFS Study of Self-Assembly of Standing 1,4-Benzenedimethanethiol SAMs on Gold . 42 [2008-064T] THERMETG.................................................................................................................................... 42 Relevance of visco-plastic theory in a multi-directional inhomogeneous granular flow .................................. 42 Experimental Evidence of a Phase Transition in a Closed Turbulent Flow ...................................................... 43 Susceptibility divergence, phase transition and multistability of a highly turbulent closed flow ..................... 43 [2008-065T] Glasdespin........................................................................................................................................ 44 Magnetic order in Tb2Sn2O7 under high pressure: From ordered spin ice to spin liquid and antiferromagnetic order .................................................................................................................................................................. 44 Field evolution of the magnetic structures in Er2Ti2O7 through the critical point ........................................... 44 Field-induced magnetic structures in Tb2Ti2O7 at low temperatures: From spin-ice to spin-flip structures ... 44 Neutron diffraction study of the chiral magnet MnGe ...................................................................................... 45 [2008-066T] OXY SPINTRONICS ...................................................................................................................... 45 Towards Two-Dimensional Metallic Behavior at LaAlO3/SrTiO3 Interfaces ................................................. 45 Ferroelectric Control of Spin Polarization ........................................................................................................ 46 Giant tunnel electroresistance with PbTiO3 ferroelectric tunnel barriers ......................................................... 46 Interface-induced room-temperature multiferroicity in BaTiO(3) .................................................................... 46 28/02/2013 4 PUBLICATIONS PROJETS 2008 Restoration of bulk magnetic properties by strain engineering in epitaxial CoFe(2)O(4) (001) ultrathin films 47 Ultrathin oxide films and interfaces for electronics and spintronics ................................................................. 47 [2008-067T] CLEL ............................................................................................................................................... 48 Seed level requirement for improving the temporal coherence of a Free-Electron Laser ................................. 48 [2008-070T] LongWave........................................................................................................................................ 48 In Situ Generation of Surface Plasmon Polaritons Using a Near-Infrared Laser Diode ................................... 48 [2008-071T] PSYCHE .......................................................................................................................................... 49 Addition of Si-Containing Gases for Anisotropic Etching of III-V Materials in Chlorine-Based Inductively Coupled Plasma................................................................................................................................................. 49 High-aspect-ratio inductively coupled plasma etching of InP using SiH4/Cl-2: Avoiding the effect of electrode coverplate material ............................................................................................................................................ 49 [2008-072T] POMS .............................................................................................................................................. 50 A PGSE-NMR Study of Molecular Self-Diffusion in Lamellar Phases Doped with Polyoxometalates ........... 50 Communications: Short-range dynamics of a nematic liquid-crystalline phase................................................ 50 Orientational Order of Colloidal Disk-Shaped Particles under Shear-Flow Conditions: a Rheological-SmallAngle X-ray Scattering Study ........................................................................................................................... 50 [2008-075T] Magnetic-Graphene ......................................................................................................................... 51 Spin-flip excitations, spin waves, and magnetoexcitons in graphene Landau levels at integer filling factors .. 51 The magnetic field particle-hole excitation spectrum in doped graphene and in a standard two-dimensional electron gas ....................................................................................................................................................... 51 Theory of Bernstein modes in graphene............................................................................................................ 52 [2008-080T] GEOFLOW ...................................................................................................................................... 52 Viscous spreading of an inertial wave beam in a rotating fluid ........................................................................ 52 Direct Measurements of Anisotropic Energy Transfers in a Rotating Turbulence Experiment ........................ 52 Excitation of inertial modes in a closed grid turbulence experiment under rotation ......................................... 53 CHEMO-hydrodynamic coupling between forced advection in porous media and self-sustained chemical waves................................................................................................................................................................. 53 Earth rotation prevents exact solid-body rotation of fluids in the laboratory .................................................... 54 Inertial waves and modes excited by the libration of a rotating cube ............................................................... 54 Relation between first arrival time and permeability in self-affine fractures with areas in contact .................. 54 Stokes flow paths separation and recirculation cells in X-junctions of varying angle ...................................... 55 [2008-082T] NonFermiSupra................................................................................................................................ 55 Hund's coupling and its key role in tuning multiorbital correlations................................................................. 55 Janus-Faced Influence of Hund's Rule Coupling in Strongly Correlated Materials .......................................... 56 Role of oxygen-oxygen hopping in the three-band copper-oxide model: Quasiparticle weight, metal insulator and magnetic phase boundaries, gap values, and optical conductivity.............................................................. 56 Covalency, double-counting, and the metal-insulator phase diagram in transition metal oxides ...................... 56 Path to poor coherence in the periodic Anderson model from Mott physics and hybridization........................ 57 [2008-086T] XDIF ................................................................................................................................................ 57 Single-shot Femtosecond X-Ray Holography Using Extended References ...................................................... 57 28/02/2013 5 PUBLICATIONS PROJETS 2008 [2008-088T] OPODRAG ...................................................................................................................................... 58 Stimulated Raman scattering in an optical parametric oscillator based on periodically poled MgO-doped stoichiometric LiTaO3 ...................................................................................................................................... 58 Frequency stabilization at the kilohertz level of a continuous intracavity frequency-doubled singly resonant optical parametric oscillator .............................................................................................................................. 58 Diode-pumped Pr:BaY(2)F(8) continuous-wave orange laser .......................................................................... 58 Sub-kHz-level relative stabilization of an intracavity doubled continuous wave optical parametric oscillator using Pound-Drever-Hall scheme ..................................................................................................................... 59 Optimization of the resonant wave output coupling of a singly resonant optical parametric oscillator using an intracavity plate ................................................................................................................................................. 59 Ultranarrow resonance due to coherent population oscillations in a Lambda-type atomic system ................... 59 [2008-091T] CAAS............................................................................................................................................... 60 Anisotropic magneto-resistance in a GaMnAs-based single impurity tunnel diode: A tight binding approach 60 Spin splitting of electron states in (110) quantum wells: Symmetry analysis and k.p theory versus microscopic calculations........................................................................................................................................................ 60 [2008-091T] CAAS 1 & [2012-019T] CAAS 2 .................................................................................................... 61 Anomalous suppression of valley splittings in lead salt nanocrystals without inversion center ....................... 61 [2008-092T] ALVAREZ....................................................................................................................................... 61 Nanostructured tantalum nitride films as buffer-layer for carbon nanotube growth ......................................... 61 [2008-095T] STP .................................................................................................................................................. 62 Electrical transport properties of Mn-doped LaFeAsO oxypnictide ................................................................. 62 Bi1-xSrxCuSeO oxyselenides as promising thermoelectric materials .............................................................. 62 Effects of Co doping on the transport properties and superconductivity in CeFe1-xCoxAsO .......................... 62 Electrical transport properties of F-doped LaFeAsO oxypnictide ..................................................................... 63 Electronic phase diagram of NdFe1-xRhxAsO ................................................................................................. 63 Superconductivity at 15 K in NdFe0.9Rh0.1AsO without F-doping ................................................................ 63 28/02/2013 6 PUBLICATIONS PROJETS 2008 [2008-002T] EEES Porteur : Jean-Pierre Gauyacq Axe B Excited electron dynamics in Cu nanowires supported on a Cu(111) surface Article publié en 2009 Auteurs : Diaz-Tendero S, Olsson FE, Borisov AG, Jean-Pierre Gauyacq Réf. : PHYSICAL REVIEW B 79 (2009) 115438 We present a theoretical study of the excited electron dynamics in infinite Cu monoatomic chains (nanowires) supported on a Cu(111) surface. A joint approach based on the wave packet propagation and the density functional theory is used. The nanowire-induced potential obtained from ab initio density functional theory calculations serves as an input for the wave-packet propagation study of the excited electron dynamics. The energy dispersion and the lifetime of an unoccupied one-dimensional (1D) nanowire-localized electronic band with sp character are obtained. From the group velocity and lifetime of the 1D sp-band states, it follows that an excited electron can travel about four to five atomic sites along the nanowire before its escape into the bulk. We show that the surface projected band gap and the surface Brillouin zone backfolding of the substrate states play a fundamental role in the lifetime of the nanowire-localized states. Extraordinary Electron Propagation Length in a Metallic Double Chain Supported on a Metal Surface Article publié en 2009 Auteurs : Diaz-Tendero S, Borisov AG, Jean-Pierre Gauyacq Réf. : PHYSICAL REVIEW LETTERS 102 (2009) 166807 PRB 83 (2011) 115453 The present theoretical study shows that a double chain of Cu metal atoms adsorbed on a Cu(111) metal surface can guide an excited electron for distances exceeding 10 nm. The nanostructure appears to be quasi-decoupled from the substrate and thus to act as a nanowire. The origin of the above phenomenon is the interference between the decay of the quasistationary 1D sp-band states localized on each chain. This allows to approach the situation of the formation of bound states in the continuum first discussed in quantum systems by von Neumann and Wigner. Mapping of the electron transmission through the wall of a quantum corral Article publié en 2009 Auteurs : Gauyacq, JP. Diaz-Tendero, S. Borisov, AG Réf. : SURFACE SCIENCE 603 (2009) 2074-2081 We report on a theoretical study of the escape of confined surface states electrons from quantum corrals made of Cu adatoms on a Cu(1 1 1) surface. This study maps electron transmission through the corral wall and provides an extension of our earlier work focused on confinement in Cu corrals [S. Diaz-Tendero, F.E. Olsson, A.G. 28/02/2013 7 PUBLICATIONS PROJETS 2008 Borisov, J.P. Gauyacq, Phys. Rev. B 77 (2008) 205403]. The existence of two decay modes for the confined surface state is stressed: (i) non-resonant tunnelling through the corral wall concentrated on the Cu adatoms and (ii) a resonant-induced decay involving the transient formation of a resonant state localized on top of the corral wall. The present mapping of the electron transmission reveals how the interference between the two decay modes works: there exist regions where the electron leaves the corral, balanced by regions where it enters the corral, though the global behaviour of the quasi-stationary states is electron escape from the corral. (C) 2009 Elsevier B.V. All rights reserved. [2008-005T] EXTREME Porteur : Jean-Paul Itié Axe A A microscopic view on the Mott transition in chromium-doped V2O3 Article publié en 2010 Auteurs : Lupi, S; Baldassarre, L; Mansart, B; Perucchi, A; Barinov, A; Dudin, P; Papalazarou, E; Rodolakis, F; Rueff, JP; Itie, JP; Ravy, S; Nicoletti, D; Postorino, P; Hansmann, P; Parragh, N; Toschi, A; Saha-Dasgupta, T; Andersen, OK; Sangiovanni, G; Held, K; Ma Réf. : NATURE COMMUNICATIONS (2010) 105 V2O3 is the prototype system for the Mott transition, one of the most fundamental phenomena of electronic correlation. Temperature, doping or pressure induce a metal-to-insulator transition (MIT) between a paramagnetic metal (PM) and a paramagnetic insulator. This or related MITs have a high technological potential, among others, for intelligent windows and field effect transistors. However the spatial scale on which such transitions develop is not known in spite of their importance for research and applications. Here we unveil for the first time the MIT in Cr-doped V2O3 with submicron lateral resolution: with decreasing temperature, microscopic domains become metallic and coexist with an insulating background. This explains why the associated PM phase is actually a poor metal. The phase separation can be associated with a thermodynamic instability near the transition. This instability is reduced by pressure, that promotes a genuine Mott transition to an eventually homogeneous metallic state. 28/02/2013 8 PUBLICATIONS PROJETS 2008 [2008-007T] QCCM Porteur : Olivier Dulieu Axe B Binary and ternary recombination of D-3(+) ions with electrons in He-D-2 plasma Article publié en 2009 Auteurs : Glosik, J. Korolov, I Plasil, R. Kotrik, T. Dohnal, P. Novotny, O. Varju, J. Roucka, S. Greene, CH. Kokoouline, V Réf. : PHYSICAL REVIEW A 80 (2009) 042706 An experimental study is reported about the recombination of D-3(+) ions with electrons in a low-temperature plasma (200-300K) consisting of He with a small admixture of D-2. At several temperatures, the pressure dependence of the apparent binary recombination rate coefficient (alpha(eff)) was measured over a broad range of helium pressures (200-2000 Pa). The binary and ternary recombination rate coefficients were obtained from measured pressure dependences of alpha(eff). The binary recombination rate coefficient obtained alpha(bin)(300 K) = (2.7 +/- 0.9) x 10(-8) cm(3) s(-1) is in agreement with recent theory. The ternary recombination rate coefficient obtained is K-He(300 K) = (1.8 +/- 0.6) x 10(-25) cm(6) s(-1). In analogy with the recently described process of helium-assisted ternary recombination of H-3(+) ions, it is suggested that the ternary helium- assisted recombination of D-3(+) ions proceeds through the formation of a neutral long- lived highly excited Rydberg molecule D-3 followed by a collision with a He atom. Binary and ternary recombination of H-3(+) and D-3(+) ions with electrons in low temperature plasma Article publié en 2010 Auteurs : Glosik, J. Plasil, R. Kotrik, T. Dohnal, P. Varju, J. Hejduk, M. Korolov, I. Roucka, S. Kokoouline, V Réf. : MOLECULAR PHYSICS 108 (2010) 2253-2264 Measurements of recombination rate coefficients of binary and ternary recombination of H-3(+) and D-3(+) ions with electrons in a low temperature plasma are described. The experiments were carried out in the afterglow plasma in helium with a small admixture of Ar and parent gas (H-2 or D-2). For both ions a linear increase of measured apparent binary recombination rate coefficients (alpha(eff)) with increasing helium density was observed: alpha(eff) = alpha(BIN) + K-He[He]. From the measured dependencies, we have obtained for both ions the binary (alpha(BIN)) and the ternary ( KHe) rate coefficients and their temperature dependence. For the description of observed ternary recombination a mechanism with two subsequent rate determining steps is proposed. In the first step, in H-3(+) + e(-) (or D-3(+) + e(-)) collision, a rotationally excited long-lived Rydberg molecule H-3(*) (or D-3(*)) is formed. In the following step H-3(*) (or D-3(*)) collides with a He atom of the buffer gas and this collision prevents autoionization of H-3(*) (or D-3(*)). Lifetimes of the formed H-3(*) (or D3(*)) and corresponding ternary recombination rate coefficients have been calculated. The theoretical and measured binary and ternary recombination rate coefficients obtained for H-3(+) and D-3(+) ions are in good agreement. 28/02/2013 9 PUBLICATIONS PROJETS 2008 Calculation of rate constants for vibrational and rotational excitation of the H+(3) ion by electron impact Article publié en 2010 Auteurs : Kokoouline, V.Faure, A. Tennyson, J. Greene, CH Réf. : MONTHLY NOTICES OF THE ROYAL ASTRONOMICAL SOCIETY 405 (2010) 1195-1202 We present theoretical thermally averaged rate constants for vibrational and rotational (de-)excitation of the H+(3) ion by electron impact. The constants are calculated using the multichannel quantum-defect approach. The calculation includes processes that involve a change |delta J| < 2 in the rotational angular momentum J of H+(3). The rate constants are calculated for states with J < 5 for rotational transitions of the H+(3) ground vibrational level. The thermal rates for transitions among the lowest eight vibrational levels are also presented, averaged over the rotational structure of the vibrational levels. The conditions for producing non-thermal rotational and vibrational distributions of H+(3) in astrophysical environments are discussed. Optical phase and the ionization-dissociation dynamics of excited H2 Article publié en 2010 Auteurs : A. Kirrander, H. H. Fielding, and Ch. Jungen Réf. : J. Chem. Phys. 132, 024313 (2010) Measurements of recombination rate coefficients of binary and ternary recombination of H-3(+) and D-3(+) ions with electrons in a low temperature plasma are described. The experiments were carried out in the afterglow plasma in helium with a small admixture of Ar and parent gas (H-2 or D-2). For both ions a linear increase of measured apparent binary recombination rate coefficients (alpha(eff)) with increasing helium density was observed: alpha(eff) = alpha(BIN) + K-He[He]. From the measured dependencies, we have obtained for both ions the binary (alpha(BIN)) and the ternary ( KHe) rate coefficients and their temperature dependence. For the description of observed ternary recombination a mechanism with two subsequent rate determining steps is proposed. In the first step, in H-3(+) + e(-) (or D-3(+) + e(-)) collision, a rotationally excited long-lived Rydberg molecule H-3(*) (or D-3(*)) is formed. In the following step H-3(*) (or D-3(*)) collides with a He atom of the buffer gas and this collision prevents autoionization of H-3(*) (or D-3(*)). Lifetimes of the formed H-3(*) (or D3(*)) and corresponding ternary recombination rate coefficients have been calculated. The theoretical and measured binary and ternary recombination rate coefficients obtained for H-3(+) and D-3(+) ions are in good agreement. Assignment of resonances in dissociative recombination of HD(+) ions: High-resolution measurements compared with accurate computations Article publié en 2011 Auteurs : Tamo, FOW; Buhr, H; Motapon, O; Altevogt, S; Andrianarijaona, VM; Grieser, M; Lammich, L; Lestinsky, M; Motsch, M; Nevo, I; Novotny, S; Orlov, DA; Pedersen, HB; Schwalm, D; Sprenger, F; Urbain, X; Weigel, U; Wolf, A; Schneider, IF Réf. : PHYSICAL REVIEW A 84 (2): 10.1103/PhysRevA.84.022710 AUG 19 2011 The collision-energy resolved rate coefficient for dissociative recombination of HD(+) ions in the vibrational ground state is measured using the photocathode electron target at the heavy-ion storage ring TSR. Rydberg resonances associated with rovibrational excitation of the HD(+) core are scanned as a function of the electron 28/02/2013 10 PUBLICATIONS PROJETS 2008 collision energy with an instrumental broadening below 1 meV in the low-energy limit. The measurement is compared to calculations using multichannel quantum defect theory, accounting for rotational structure and interactions and considering the six lowest rotational energy levels as initial ionic states. Using thermalequilibrium-level populations at 300 K to approximate the experimental conditions, close correspondence between calculated and measured structures is found up to the first vibrational excitation threshold of the cations near 0.24 eV. Detailed assignments, including naturally broadened and overlapping Rydberg resonances, are performed for all structures up to 0.024 eV. Resonances from purely rotational excitation of the ion core are found to have similar strengths as those involving vibrational excitation. A dominant low-energy resonance is assigned to contributions from excited rotational states only. The results indicate strong modifications in the energy dependence of the dissociative recombination rate coefficient through the rotational excitation of the parent ions, and underline the need for studies with rotationally cold species to obtain results reflecting lowtemperature ionized media. Electron collisions with BF+: bound and continuum states of BF Article publié en 2011 Auteurs : Chakrabarti K; Schneider, IF; Tennyson, J Réf. : JOURNAL OF PHYSICS B-ATOMIC MOLECULAR AND OPTICAL PHYSICS 44 (5) 055203 (2011) Rydberg and continuum states of the BF molecule are studied as a function of geometry using an electron collision formalism in the framework of the R-matrix method. Up to 14 BF+ target states are used in a closecoupling expansion and bound states are searched for as negative energy solutions of the scattering calculation. Potential energy curves and quantum defects are obtained for the excited states of BF. Resonance positions and widths are also calculated for Feshbach resonances in the system. The data obtained can be used to model dissociative recombination of the BF+ molecular ion. Formation of the simplest stable negative molecular ion H3- in interstellar medium Article publié en 2011 Auteurs : M. Ayouz, R. Lopez, M. Raoult, J. Robert, O. Dulieu, V. Kokoouline Réf. : Phys. Rev. A. 83, 052712 (2011) We develop the theory of radiative association of an atom and a diatomic molecule within a close-coupling framework. We apply it to the formation of H-3(-) after the low-energy collision (below 0.5 eV) of H-2 with H-. Using recently obtained potential energy and permanent dipole moment surfaces of H-3(-), we calculate the lowest rovibrational levels of the H-3(-) electronic ground state and the cross section for the formation of H-3(-) by radiative association between H- and ortho- and para-H-2. We discuss the possibility for the H-3(-) ion to be formed and observed in the cold and dense interstellar medium in an environment with a high ionization rate. Such an observation could be a probe for the presence of H- in the interstellar medium. Laser control of complete vibrational transfer in Na2 using resonance coalescence Article publié en 2011 Auteurs : O. Atabek, R. Lefebvre, M. Lepers, A. Jaouadi, O. Dulieu, and V. Kokoouline Réf. : Phys. Rev. Lett. 106, 173002 (2011) Rydberg and continuum states of the BF molecule are studied as a function of geometry using an electron collision formalism in the framework of the R-matrix method. Up to 14 BF+ target states are used in a closecoupling expansion and bound states are searched for as negative energy solutions of the scattering calculation. 28/02/2013 11 PUBLICATIONS PROJETS 2008 Potential energy curves and quantum defects are obtained for the excited states of BF. Resonance positions and widths are also calculated for Feshbach resonances in the system. The data obtained can be used to model dissociative recombination of the BF+ molecular ion. Laser cooling of the vibrational motion of Na(2) combining the effects of zero-width resonances and exceptional points Article publié en 2011 Auteurs : R. Lefebvre, A. Jaouadi, O. Dulieu, O. Atabek Réf. : PHYSICAL REVIEW A Volume: 84 Issue: 4 10.1103/PhysRevA.84.043428 Published: OCT 24 2011 Article Number: 043428 DOI: We propose various scenarios for molecular vibrational cooling combining the effects of two kinds of resonance states occurring during the photodissociation of Na(2) taken as an illustrative example. Such resonances result from an appropriate sampling of laser parameters (wavelength and intensity): (a) For particular choices of intensity and wavelength, two resonance energies can be brought to complete coalescence, with their positions and widths becoming equal and leading to a so-called exceptional point (EP) in the parameter plane. Advantage can be taken from such points for very selective laser-controlled vibrational transfer strategies. (b) For specific intensities, far beyond the perturbation regime, some resonances can have a zero width (infinite lifetime). They are referred to as a zero-width resonance (ZWR) and may be used for vibrational purification purposes. We show how appropriately shaped, experimentally reachable laser pulses, encircling EPs or inducing ZWRs, may be used for a thorough and comprehensive control aiming at population transfer or purification schemes, which, starting from an initial field-free vibrational distribution, ends up in the ground vibrational level. Photoassociation of a cold-atom-molecule pair. II. Second-order perturbation approach Article publié en 2011 Auteurs : Lepers, M; Vexiau, R; Bouloufa, N; Olivier Dulieu; Kokoouline, V Réf. : PHYSICAL REVIEW A 83 (2011) 042707 The electrostatic interaction between an excited atom and a diatomic ground-state molecule in an arbitrary rovibrational level at large mutual separations is investigated with a general second-order perturbation theory, in the perspective of modeling the photoassociation between cold atoms and molecules. We find that the combination of quadrupole-quadrupole and van der Waals interactions competes with the rotational energy of the dimer, limiting the range of validity of the perturbative approach to distances larger than 100 Bohr radii. Numerical results are given for the long-range interaction between Cs and Cs-2, showing that the photoassociation is probably efficient for any Cs-2 rotational energy. Proposal for a Laser Control of Vibrational Cooling in Na-2 Using Resonance Coalescence Article publié en 2011 Auteurs : Atabek O, Lefebvre R, Lepers M, Jaouadi A, Olivier Dulieu, Kokoouline V Réf. : PHYSICAL REVIEW LETTERS 106 (17): Art. No. 173002 APR 29 2011 With a specific choice of laser parameters resulting in a so-called exceptional point (EP) in the wavelengthintensity parameter plane, it is possible to produce the coalescence of two Floquet resonances describing the photodissociation of the Na-2 molecule, which is one of the candidates for the formation of samples of translationally cold molecules. By appropriately tuning laser parameters along a contour encircling the 28/02/2013 12 PUBLICATIONS PROJETS 2008 exceptional point, the resonances exchange their quantum nature. Thus a laser-controlled transfer of the probability density from one field-free vibrational level to another is achieved through adiabatic transport involving these resonances. We propose an efficient scenario for vibrational cooling of Na-2 referring to cascade transfers involving multiple EPs and predicted to be robust up to a 78% rate against laser-induced dissociation. Triplet-singlet conversion in ultracold Cs-2 and production of ground-state molecules Article publié en 2011 Auteurs : Bouloufa, N; Pichler, M; Aymar, M; Olivier Dulieu Réf. : PHYSICAL REVIEW A 83 (2011) 022503 We propose a process to convert ultracold metastable Cs-2 molecules in their lowest triplet state into (singlet) ground-state molecules in their lowest vibrational levels. Molecules are first pumped into an excited triplet state, and the triplet-singlet conversion is facilitated by a two-step spontaneous decay through the coupled A(1)Sigma(+)(u)-b(3)Pi(u) states. Using spectroscopic data and accurate quantum chemistry calculations for Cs2 potential curves and transition dipole moments, we show that this process competes favorably with the singlephoton decay back to the lowest triplet state. In addition, we demonstrate that this conversion process represents a loss channel for vibrational cooling of metastable triplet molecules, preventing an efficient optical pumping cycle down to low vibrational levels. Breaking a tetrahedral molecular ion with electrons: study of NH4+ Article publié en 2012 Auteurs : Douguet N.; Kokoouline V.; Orel A. E. Réf. : JOURNAL OF PHYSICS B-ATOMIC MOLECULAR AND OPTICAL PHYSICS Volume: 45 Issue: 5 Article Number: 051001 DOI: 10.1088/0953-4075/45/5/051001 Published: MAR 14 2012 We apply a general theoretical model to study the dissociative recombination of the polyatomic ion NH4+. The high symmetry of the molecule, represented by the tetrahedral group, leads to complex vibronic couplings responsible for dissociative recombination. By applying multi-channel quantum defect theory and using symmetry considerations, we treat the doubly and triply degenerate modes and electronic states of NH4+ to calculate a theoretical cross section. The cross section agrees well with existing experimental data. Potential energy and dipole moment surfaces of HCO- for the search of H- in the interstellar medium Article publié en 2012 Auteurs : Ayouz, M.; Mikhailov, I.; Babikov, D.; Raoult, M.; Galtier, S.; Dulieu, O.; Kokoouline, V. Réf. : JOURNAL OF CHEMICAL PHYSICS Volume: 136 10.1063/1.4724096 Published: JUN 14 2012 Issue: 22 Article Number: 224310 DOI: Potential energy and permanent dipole moment surfaces of the electronic ground state of formyl negative ion HCO- are determined for a large number of geometries using the coupled-cluster theory with single and double and perturbative treatment of triple excitations ab initio method with a large basis set. The obtained data are used to construct interpolated surfaces, which are extended analytically to the region of large separations between CO and H- with the multipole expansion approach. We have calculated the energy of the lowest rovibrational levels of HCO- that should guide the spectroscopic characterization of HCO- in laboratory experiments. The study can also help to detect HCO- in the cold and dense regions of the interstellar medium where the anion could be formed through the association of abundant CO with still unobserved H-. (C) 2012 American Institute of Physics. [http://dx.doi.org/10.1063/1.4724096] 28/02/2013 13 PUBLICATIONS PROJETS 2008 Photoassociation of a cold-atom-molecule pair: Long-range quadrupole-quadrupole interactions Article publié en 2010 Auteurs : Lepers M, Olivier Dulieu, Kokoouline V Réf. : PHYSICAL REVIEW A 82 (2010) 042711 The general formalism of the multipolar expansion of electrostatic interactions is applied to the calculation of the potential energy between an excited atom (without fine structure) and a ground-state diatomic molecule at large mutual separations. Both partners exhibit a permanent quadrupole moment so that their mutual long-range interaction is dominated by a quadrupole-quadrupole term, which is attractive enough to bind trimers. Numerical results are given for an excited Cs(6(2)P) atom and a ground-state Cs-2 molecule. The prospects for achieving photoassociation of a cold-atom-dimer pair are thus discussed and found promising. The formalism can be generalized to the long-range interaction between molecules to investigate the formation of cold tetramers. Cold atom-molecule photoassociation: long-range interactions beyond the 1/Rn expansion Article publié en 2011 Auteurs : M. Lepers, O. Dulieu Réf. : Eur. Phys. J. D 10.1140/epjd/e2011-20083-6 (2011) We present a theoretical description of dissociative recombination of triatomic molecular ions having large permanent dipole moments. The study has been partly motivated by a discrepancy between experimental and theoretical cross sections for dissociative recombination of the HCO+ ion. The HCO+ ion has a considerable permanent dipole moment (D approximate to 4 D), which has not been taken explicitly into account in previous theoretical studies. In the present study, we include explicitly the effect of the permanent electric dipole on the dynamics of the incident electron using the generalized quantum defect theory, and we present the resulting cross section obtained. This demonstrates the possibility of applying generalized quantum defect theory to the dissociative recombination of molecular ions. Laser cooling of the vibrational motion of Na2 combining the effects of Zero Width Resonances and Exceptional Points. Article publié en 2011 Auteurs : R. Lefebvre, A. Jouadi, O. Dulieu, O. Atabek Réf. : Phys. Rev. A. in press 84 (2011) 043428 We present a theoretical description of dissociative recombination of triatomic molecular ions having large permanent dipole moments. The study has been partly motivated by a discrepancy between experimental and theoretical cross sections for dissociative recombination of the HCO+ ion. The HCO+ ion has a considerable permanent dipole moment (D approximate to 4 D), which has not been taken explicitly into account in previous theoretical studies. In the present study, we include explicitly the effect of the permanent electric dipole on the dynamics of the incident electron using the generalized quantum defect theory, and we present the resulting cross section obtained. This demonstrates the possibility of applying generalized quantum defect theory to the dissociative recombination of molecular ions. 28/02/2013 14 PUBLICATIONS PROJETS 2008 Long-range interactions between ultracold atoms and molecules including atomic spin-orbit Article publié en 2011 Auteurs : M. Lepers, O. Dulieu Réf. : Phys. Chem. Chem. Phys. In press We present a theoretical description of dissociative recombination of triatomic molecular ions having large permanent dipole moments. The study has been partly motivated by a discrepancy between experimental and theoretical cross sections for dissociative recombination of the HCO+ ion. The HCO+ ion has a considerable permanent dipole moment (D approximate to 4 D), which has not been taken explicitly into account in previous theoretical studies. In the present study, we include explicitly the effect of the permanent electric dipole on the dynamics of the incident electron using the generalized quantum defect theory, and we present the resulting cross section obtained. This demonstrates the possibility of applying generalized quantum defect theory to the dissociative recombination of molecular ions. Photoassociation of a cold atom-molecule pair II: second-order perturbation approach Article publié en 2011 Auteurs : M. Lepers, O. Dulieu, V. Kokoouline Réf. : Phys Rev. A 83, 042707 (2011) We present a theoretical description of dissociative recombination of triatomic molecular ions having large permanent dipole moments. The study has been partly motivated by a discrepancy between experimental and theoretical cross sections for dissociative recombination of the HCO+ ion. The HCO+ ion has a considerable permanent dipole moment (D approximate to 4 D), which has not been taken explicitly into account in previous theoretical studies. In the present study, we include explicitly the effect of the permanent electric dipole on the dynamics of the incident electron using the generalized quantum defect theory, and we present the resulting cross section obtained. This demonstrates the possibility of applying generalized quantum defect theory to the dissociative recombination of molecular ions. Potential energy and dipole moment surfaces of HCO- for the search of H- in the interstellar medium Article publié en 2012 Auteurs : Ayouz M.; Mikhailov I.; Babikov D.; et al. Réf. : JOURNAL OF CHEMICAL PHYSICS Volume: 136 10.1063/1.4724096 Published: JUN 14 2012 Issue: 22 Article Number: 224310 DOI: Potential energy and permanent dipole moment surfaces of the electronic ground state of formyl negative ion HCO- are determined for a large number of geometries using the coupled-cluster theory with single and double and perturbative treatment of triple excitations ab initio method with a large basis set. The obtained data are used to construct interpolated surfaces, which are extended analytically to the region of large separations between CO and H- with the multipole expansion approach. We have calculated the energy of the lowest rovibrational levels of HCO- that should guide the spectroscopic characterization of HCO- in laboratory experiments. The study can also help to detect HCO- in the cold and dense regions of the interstellar medium where the anion could be formed through the association of abundant CO with still unobserved H-. (C) 2012 American Institute of Physics. [http://dx.doi.org.gate4.inist.fr/10.1063/1.4724096] 28/02/2013 15 PUBLICATIONS PROJETS 2008 Theory of dissociative recombination of a linear triatomic ion with permanent electric dipole moment: Study of HCO+ Article publié en 2009 Auteurs : Douguet, N. Kokoouline, V. Greene, CH Réf. : PHYSICAL REVIEW A 80 (2009) 062712 We present a theoretical description of dissociative recombination of triatomic molecular ions having large permanent dipole moments. The study has been partly motivated by a discrepancy between experimental and theoretical cross sections for dissociative recombination of the HCO+ ion. The HCO+ ion has a considerable permanent dipole moment (D approximate to 4 D), which has not been taken explicitly into account in previous theoretical studies. In the present study, we include explicitly the effect of the permanent electric dipole on the dynamics of the incident electron using the generalized quantum defect theory, and we present the resulting cross section obtained. This demonstrates the possibility of applying generalized quantum defect theory to the dissociative recombination of molecular ions. [2008-015T] ULYSSE & [2009-004T] ULYSSE II Porteur : Yong Jin Thème 1 Insight into low frequency noise induced by gate leakage current in AlGaAs/GaAs high electron mobility transistors at 4.2 K Article publié en 2011 Auteurs : Liang, YX; Dong, Q; Cheng, MC; Gennser, U; Cavanna, A; Jin, Y Réf. : APPLIED PHYSICS LETTERS 99 (11): 10.1063/1.3637054 SEP 12 2011 The bias-cooling method-the gate being kept biased at V(gc) during the cooling-has been used to investigate the low frequency noise (LFN) in an AlGaAs/GaAs two-dimensional electron gas high electron mobility transistor at 4.2 K. For a chosen working point (i.e., a chosen drain bias/current), its gate bias V(gs), gate leakage current I(gs), and LFN depend on V(gc). With the help of the heterostructure band diagram simulation for each V(gc), the relation between I(gs) and the LFN can be elucidated by the gate Fermi level with regard to the heterostructure band diagram. The LFN originated from I(gs) is caused by its sequential tunnelling component. (C) 2011 American Institute of Physics. [doi:10.1063/1.3637054] Input Noise Voltage Below 1 nV/Hz(1/2) at 1 kHz in the HEMTs at 4.2 K Article publié en 2012 Auteurs : Liang, Y. X.; Dong, Q.; Gennser, U.; Cavanna, A.; Jin, Y. Réf. : JOURNAL OF LOW TEMPERATURE PHYSICS Volume: 167 Issue: 5-6 Pages: 632-637 DOI: 10.1007/s10909-012-0479-9 Part: Part 2 Published: JUN 2012 28/02/2013 16 PUBLICATIONS PROJETS 2008 Specific High Electron Mobility Transistors (HEMTs) have been realized and characterized. At 4.2 K, with a drain-source current I (ds) of 1.55 mA and drain-source voltage V (ds) of 100 mV, the transistor has the following electrical characteristics: a transconductance and an output conductance of 69 and 3.8 mS, respectively, leading to an intrinsic voltage gain of 18; an input gate-source capacitance C (gs) of about 31 pF; and a gate leakage current less than 0.2 pA. An equivalent input noise voltage lower than 1 nV/Hz(1/2) at 1 kHz has been achieved when I (ds)=1.55 mA at V (ds)=100 mV. Hence, our results show that the specific HEMTs should be a suitable transistor for future ultra-low noise deep cryogenic low-frequency high-impedance readout electronics. The Role of the Gate Geometry for Cryogenic HEMTs: Towards an Input Voltage Noise Below 0.5 nV/root Hz at 1 kHz and 4.2 K Article publié en 2012 Auteurs : Dong, Q.; Liang, Y. X.; Gennser, U.; Cavanna, A.; Jin, Y. Réf. : JOURNAL OF LOW TEMPERATURE PHYSICS Volume: 167 Issue: 5-6 Pages: 626-631 DOI: 10.1007/s10909-012-0459-0 Part: Part 2 Published: JUN 2012 Specific HEMTs (High Electron Mobility Transistors) with different gate geometries have been realized on the same AlGaAs/GaAs heterojunction. Under the same operating conditions with a power consumption of 30 mu w, experimental results at 4.2 K and low frequency range show that the input voltage noise is almost inversely proportional to the square root of the input capacitance: a noise value as low as 0.46 nV/v Hz at 1 kHz has been obtained with an input capacitance of about 100 pF. [2008-016T] SMGM Porteur : Olivier Dauchot Thème 3 Elementary excitation modes in a granular glass above jamming Article publié en 2010 Auteurs : Brito, C. Olivier Dauchot. Biroli, G. Bouchaud, JP Réf. : SOFT MATTER 6 (2010) 3013-3022 The dynamics of granular media in the jammed, glassy region is described in terms of "modes'', by applying a principal component analysis (PCA) to the covariance matrix of the position of individual grains. We first demonstrate that this description is justified and gives sensible results in a regime of time/densities such that a metastable state can be observed on a long enough timescale to define the reference configuration. For small enough times/system sizes, or at high enough packing fractions, the spectral properties of the covariance matrix reveals large, collective fluctuation modes that cannot be explained by a random matrix benchmark where these correlations are discarded. We then present a first attempt to find a link between the softest modes of the covariance matrix during a certain "quiet'' time interval and the spatial structure of the rearrangement event that ends this quiet period. The motion during these cracks is indeed well explained by the soft modes of the dynamics before the crack, but the number of cracks preceded by a "quiet'' period strongly reduces when the system unjams, questioning the relevance of a description in terms of modes close to the jamming transition, at least for frictional grains. 28/02/2013 17 PUBLICATIONS PROJETS 2008 [2008-019T] MCQM Porteur : Rosa Tualle-Brouri Thème 1 Multiple-measurement Leggett-Garg inequalities Article publié en 2009 Auteurs : Barbieri, M Réf. : PHYSICAL REVIEW A 80 (2009) 034102 In the investigation of the quantum to classical transition, the Leggett-Garg inequality represents what Bell's inequality is for the study of entanglement and nonlocality: a definite quantitative test showing the inadequacy of familiar lines of thought in interpreting quantum phenomena. Here we discuss the generalization of the LeggettGarg inequality to an arbitrary number of measurements in the perspective of its use as a tool for characterizing nondestructive measurement devices. Implementation of a Nondeterministic Optical Noiseless Amplifier Article publié en 2010 Auteurs : Ferreyrol, F. Barbieri, M. Blandino, R. Fossier, S. Rosa Tualle-Brouri.Grangier, P Réf. : PHYSICAL REVIEW LETTERS 104 (2010) 123603 Quantum mechanics imposes that any amplifier that works independently on the phase of the input signal has to introduce some excess noise. The impossibility of such a noiseless amplifier is rooted in the unitarity and linearity of quantum evolution. A possible way to circumvent this limitation is to interrupt such evolution via a measurement, providing a random outcome able to herald a successful-and noiseless-amplification event. Here we show a successful realization of such an approach; we perform a full characterization of an amplified coherent state using quantum homodyne tomography, and observe a strong heralded amplification, with about a 6 dB gain and a noise level significantly smaller than the minimal allowed for any ordinary phase-independent device. Nondeterministic noiseless amplification of optical signals: a review of recent experiments Article publié en 2011 Auteurs : Barbieri, M, Ferreyrol, F, Blandino, R, Rosa Tualle-Brouri, Grangier, P Réf. : LASER PHYSICS LETTERS 8 (6): 411-417 JUN 2011 Linear amplifiers necessarily introduce a minimal amount of noise, as required by Heisenberg's relation in quantum mechanics. Such a limitation could be overcome when considering nondeterminsitic processes, heralded by a trigger event. Here we present a review of implementations of this technique, which have recently appeared in the literature. 28/02/2013 18 PUBLICATIONS PROJETS 2008 [2008-020T] MICROHALL Porteur : Denis L'Hôte Axe A A local noise measurement device for magnetic physical systems Article publié en 2009 Auteurs : L'Hote D, Nakamae S, Ladieu F, Mosser V, Kerlain A, Konczykowski M Réf. : JOURNAL OF STATISTICAL MECHANICS-THEORY AND EXPERIMENT (2009) P01027 We present an experimental setup developed to measure locally the fluctuations of the magnetization of physical systems such as spin and superspin glasses. It is based on micronic and submicronic Hall probes. We present the noise reduction at ambient temperature owing to the use of the spinning current technique. Finally, we show why, with such probes, the noise measured on a macroscopic sample probes only a microscopic volume of the sample. [2008-025T] FLUCT-DMABN Porteur : Thomas Gustavsson Thème 2 Do fluorescence and transient absorption probe the same intramolecular charge transfer state of 4(dimethylamino)benzonitrile? Article publié en 2009 Auteurs : Gustavsson, T. Coto, PB. Serrano-Andres, L. Fujiwara, T. Lim, EC Réf. : JOURNAL OF CHEMICAL PHYSICS 131 (2009) 031101 We present here the results of time-resolved absorption and emission experiments for 4(dimethylamino)benzonitrile in solution, which suggest that the fluorescent intramolecular charge transfer (ICT) state may differ from the twisted ICT (TICT) state observed in transient absorption. Intramolecular charge transfer and dual fluorescence of 4(dimethylamino) benzonitrile: ultrafast branching followed by a two-fold decay mechanism Article publié en 2011 Auteurs : Coto, Pedro B.; Serrano-Andres, Luis; Gustavsson, Thomas; Fujiwara, Takashige; Lim, Edward C. Réf. : PHYSICAL CHEMISTRY CHEMICAL PHYSICS 13 (33): 15182-15188 10.1039/c1cp21089k 2011 28/02/2013 19 PUBLICATIONS PROJETS 2008 In this contribution we present new experimental and theoretical results for the intramolecular charge transfer (ICT) reaction underlying the dual fluorescence of 4-(dimethylamino) benzonitrile ( DMABN), which indicate that the fully twisted ICT (TICT) state is responsible for the time-resolved transient absorption spectrum while a distinct partially twisted ICT (pTICT) structure is suggested for the fluorescent ICT state. [2008-026T] Prodymag Porteur : J. Ferré/A. Thiaville Axe B Dynamic fluctuations and two-dimensional melting at the spin reorientation transition Article publié en 2012 Auteurs : Bergeard, N. (1,2); Jamet, JP (1); Mougin, A (1); Ferre, J (1); Gierak, J (3); Bourhis, E (3); Stamps, R (4) Réf. : PHYSICAL REVIEW B Volume: 86 Issue: 9 10.1103/PhysRevB.86.094431 Published: SEP 25 2012 Article Number: 094431 DOI: Instabilities and strong spatiotemporal fluctuations in out-of-plane demagnetized stripe domain patterns of a Pt/Co(0.5 nm)/Pt film designed by Ga+ ion irradiation were visualized by polar magneto-optical Kerr effect microscopy and studied in the spin reorientation transition temperature region. A two-dimensional-stripe melting transition was evidenced before reaching the in-plane spin state. Slow dynamics were driven by short-range instabilities on magnetic defects which trigger long-range transverse wall fluctuations. The spatial and temporal behavior of stripelike "floating" patches was investigated. Dynamics cannot be simply interpreted by models previously proposed for liquid crystals. [2008-027T] POMICO Porteur : Jean Daillant Axe B Organization of Block Copolymers using NanoImprint Lithography: Comparison of Theory and Experiments Article publié en 2011 Auteurs : Man, XK; Andelman, D; Orland, H; Thebault, P; Liu, PH; Guenoun, P; Jean Daillant; Landis, S Réf. : MACROMOLECULES 44 (2011) 2206-2211 We present NanoImprint lithography experiments and modeling of thin films of block copolymers (BCP). The NanoImprint technique is found to be an efficient tool not only to align lamellar phases perpendicularly to the 28/02/2013 20 PUBLICATIONS PROJETS 2008 substrate but also to get rid of in-plane defects over distances much larger than the natural lamellar periodicity. The modeling relies on self-consistent field calculations done in two- and three-dimensions and is found to be in good agreement with the experiments. It also offers some insight on the Nanolmprint lithography setup and on the conditions required to perfectly ordered BCP lamellae. Tailoring Nanostructures Using Copolymer Nanoimprint Lithography Article publié en 2012 Auteurs : Thebault Pascal; Niedermayer Stefan; Landis Stefan; et al. Réf. : ADVANCED MATERIALS Volume: 24 10.1002/adma.201103532 Published: APR 17 2012 Issue: 15 Pages: 1952-1955 DOI: Pas d'abstract Block Copolymer at Nano-Patterned Surfaces Article publié en 2010 Auteurs : Man XK, Andelman D, Orland H Réf. : MACROMOLECULES 43 (2010) We present numerical calculations of lamellar phases of block copolymers at patterned surfaces. We model symmetric diblock copolymer films forming lamellar phases and the effect of geometrical and chemical surface patterning on the alignment and orientation of lamellar phases. The calculations are done within self-consistent field theory (SCFT), where the semi-implicit relaxation scheme is used to solve the diffusion equation. Two specific setups, motivated by recent experiments, are investigated. In the first, the film is placed on top of a surface imprinted with long chemical stripes. The stripes interact more favorably with one of the two blocks and induce a perpendicular orientation in a large range of system parameters. However, the system is found to be sensitive to its initial conditions and sometimes gets trapped into a metastable mixed state composed of domains in parallel and perpendicular orientations. In a second setup, we study the film structure and orientation when it is pressed against a hard grooved mold. The mold surface prefers one of the two components, and this setup is found to be superior for inducing a perfect perpendicular lamellar orientation for a wide range of system parameters. [2008-028T] MASLOV Porteur : Montambaux, G Thème 4 Nonanalytic Spin Susceptibility of a Fermi Liquid: The Case of FeBased Pnictides Article publié en 2009 Auteurs : Korshunov, MM. Eremin, I. Efremov, DV. Maslov, DL. Chubukov, AV Réf. : PHYSICAL REVIEW LETTERS 102 (2009) 236403 28/02/2013 21 PUBLICATIONS PROJETS 2008 We propose an explanation of the peculiar linear temperature dependence of the uniform spin susceptibility chi(T) in ferropnictides. We argue that the linear in T term appears to be due to the nonanalytic temperature dependence of chi(T) in a two-dimensional Fermi liquid. We show that the prefactor of the T term is expressed via the square of the spin-density-wave (SDW) amplitude connecting nested hole and electron pockets. Because of an incipient SDW instability, this amplitude is large, which, along with a small value of the Fermi energy, makes the T dependence of chi(T) strong. We demonstrate that this mechanism is in quantitative agreement with the experiment. [2008-029T] HY-IRGS-2 Porteur : Eric Vincent Axe B Emergence of Rigidity at the Structural Glass Transition: A FirstPrinciples Computation Article publié en 2010 Auteurs : Yoshino, H. Mezard, M Réf. : PHYSICAL REVIEW LETTERS 105 (2010) 015504 We compute the shear modulus of structural glasses from a first-principles approach based on the cloned liquid theory. We find that the intrastate shear modulus, which corresponds to the plateau modulus measured in linear viscoelastic measurements, strongly depends on temperature and vanishes continuously when the temperature is increased beyond the glass temperature. Replica theory of the rigidity of structural glasses Article publié en 2012 Auteurs : Yoshino, Hajime Réf. : JOURNAL OF CHEMICAL PHYSICS Volume: 136 10.1063/1.4722343 Published: JUN 7 2012 Issue: 21 Article Number: 214108 DOI: We present a first principle scheme to compute the rigidity, i.e., the shear-modulus of structural glasses at finite temperatures using the cloned liquid theory, which combines the replica theory and the liquid theory. With the aid of the replica method which enables disentanglement of thermal fluctuations in liquids into intra-state and inter-state fluctuations, we extract the rigidity of metastable amorphous solid states in the supercooled liquid and glass phases. The result can be understood intuitively without replicas. As a test case, we apply the scheme to the supercooled and glassy state of a binary mixture of soft-spheres. The result compares well with the shearmodulus obtained by a previous molecular dynamic simulation. The rigidity of metastable states is significantly reduced with respect to the instantaneous rigidity, namely, the Born term, due to non-affine responses caused by displacements of particles inside cages at all temperatures down to T = 0. It becomes nearly independent of temperature below the Kauzmann temperature T-K. At higher temperatures in the supercooled liquid state, the non-affine correction to the rigidity becomes stronger suggesting melting of the metastable solid state. Inter-state part of the static response implies jerky, intermittent stress-strain curves with static analogue of yielding at mesoscopic scales. (C) 2012 American Institute of Physics. [http://dx.doi.org/10.1063/1.4722343] 28/02/2013 22 PUBLICATIONS PROJETS 2008 [2008-031T] STOLTE Porteur : Benoît Soep Thème 2 Unusual Quantum Interference in the S-1 State of DABCO and Observation of Intramolecular Vibrational Redistribution Article publié en 2010 Auteurs : Poisson, L. Maksimenska, R. Soep, B. Jean-Michel Mestdagh. Parker, DH. Nsangou, M.Hochlaf, M Réf. : JOURNAL OF PHYSICAL CHEMISTRY A 114 (2010) 11269-11276 In this paper we report an experimental study of the time-resolved response of the molecule 1,4diazabicyclo[2.2.2]octane (DABCO) to 266.3 nm electronic excitation of the S-1 state with a femtosecond laser. Rotational decoherence and vibrational oscillation within the S-1 state are observed. We performed state-of-theart ab initio calculations on the ground and low electronic states of the neutral molecule and the cation, which assist in the assignment of the observed photoelectron signals. Using our theoretical and spectroscopic data, the experimental findings are interpreted in terms of an unusual quantum interference between two different vibrational modes, with only the v = 1 level of each mode being populated. [2008-032T] B-DIAMANT Porteur : Jean-François Roch Thème 7 Influence of a static magnetic field on the photoluminescence of an ensemble of nitrogen-vacancy color centers in a diamond singlecrystal Article publié en 2009 Auteurs : Lai ND, Zheng DW, Jelezko F, Treussart F, Roch JF Réf. : APPLIED PHYSICS LETTERS 95 (2009) 133101 We investigate the electron spin resonance of an ensemble of nitrogen-vacancy (NV) color centers in a bulk diamond crystal. The four possible orientations of the NV center in the lattice lead to different dependences on the magnitude and the orientation of an external static magnetic field. Experimental results obtained with a continuous microwave excitation are in good agreement with simulations. In addition, we observe that the average radiative lifetime of the NV color center is also modified when the external magnetic field is applied. This variation is explained by the mixing between m(S)=0 and m(S)=+/- 1 spin states of the NV center with different radiative lifetimes, due to magnetic coupling. These results are of interest for a broad range of applications, such as spin-resonance-based magnetometry with a high-density ensemble of NV centers. (C) 2009 American Institute of Physics. 28/02/2013 23 PUBLICATIONS PROJETS 2008 Avoiding power broadening in optically detected magnetic resonance of single NV defects for enhanced dc magnetic field sensitivity Article publié en 2011 Auteurs : A Dreau, M Lesik, L Rondin, P Spinicelli, O Arcizet, JF Roch, V Jacques Réf. : PHYSICAL REVIEW B, 84 (19):10.1103/PhysRevB.84.195204 NOV 23 2011 We report a systematic study of the magnetic field sensitivity of a magnetic sensor consisting of a single nitrogen-vacancy (NV) defect in diamond, by using continuous optically detected electron spin resonance (ESR) spectroscopy. We first investigate the behavior of the ESR contrast and linewidth as a function of the microwave and optical pumping power. The experimental results are in good agreement with a simplified model of the NV defect spin dynamics, leading to an optimized sensitivity around 2 mu T/root Hz for a single NV defect in a high-purity diamond crystal grown by chemical vapor deposition. We then demonstrate an enhancement of the magnetic sensitivity by one order of magnitude by using a simple pulsed-ESR scheme. This technique is based on repetitive excitation of the NV defect with a resonant microwave pi pulse followed by an optimized readout laser pulse, allowing to fully eliminate power broadening of the ESR linewidth. The achieved sensitivity is similar to that obtained by using Ramsey-type sequences, which is the optimal magnetic field sensitivity for the detection of a dc magnetic field. [2008-046T] DYNELEC Porteur : Danielle Dowek Thème 2 Ion Pair Formation in Multiphoton Excitation of NO2 Using Linearly and Circularly Polarized Femtosecond Light Pulses: Kinetic Energy Distribution and Fragment Recoil Anisotropy Article publié en 2010 Auteurs : Elkharrat, C. Picard, YJ. Billaud, P. Cornaggia, C. Garzella, D. Perdrix, M. Houver, JC. Lucchese, RR. Dowek, D Réf. : JOURNAL OF PHYSICAL CHEMISTRY A 114 (2010) 9902-9918 The NO2 ion pair photodissociation dynamics leading to NO+ (X-1 Sigma(+), v) + O-(P-2(3/2) or P-2(1/2)), induced by a 1 kHz fermtosecond laser with wavelengths near 400 nm, has been characterized using the coincidence vector correlation method. The ion pair production after four-photon absorption reaches more than 15% of the primary ionization. The kinetic energy release of the fragments demonstrates a significant vibrational excitation of the NO+ (X-1 Sigma(+), v) molecular fragment. Recoil ion fragment emission is strongly aligned along the polarization axis of linearly polarized light or preferentially emitted in the plane perpendicular to the propagation axis of circularly polarized light. The formalism describing the recoil anisotropy for bound-to-bound n-photon transition inducing prompt axial recoil dissociation of a nonlinear molecule has been developed to interpret the measured anisotropies in terms of excitation pathways via near-resonant intermediate states of specific symmetries. Possible reaction pathways are discussed that are consistent with the data and supported by calculations of potential energy surfaces and transition moments. 28/02/2013 24 PUBLICATIONS PROJETS 2008 Molecular frame photoemission in dissociative ionization of H-2 and D-2 induced by high harmonic generation femtosecond XUV pulses Article publié en 2012 Auteurs : Billaud, P. (1,2); Geleoc, M. (3); Picard, YJ (1,2); Veyrinas, K (1,2); Hergott, JF (3); Poullain, SM (1,2); Breger, P (3); Ruchon, T (3); Roulliay, M (1,2); Delmotte, F (4); Lepetit, F (3); Huetz, A (1,2); Carre, B (3); Dowek, D (1,2) Réf. : JOURNAL OF PHYSICS B-ATOMIC MOLECULAR AND OPTICAL PHYSICS Volume: 45 Issue: 19 Special Issue: SI Article Number: 194013 DOI: 10.1088/0953-4075/45/19/194013 Published: OCT 14 2012 We report the first results of molecular frame photoelectron emission for dissociative photoionization (DPI) of H-2 and D-2 molecules induced by a spectrally filtered single high harmonic of a few femtosecond duration, using coincident electron-ion velocity vector correlation techniques. For the studied photon energies around 32 eV, where the resonant excitation of the Q(1) and Q(2) doubly excited states occurs, autoionization and nuclear dynamics are coupled on a few femtosecond timescale, giving rise to quantum interferences. Molecular frame photoelectron angular distributions (MFPADs), traced as a function of the kinetic energy release of the atomic fragments, provide the most sensitive observables for such complex dynamics. These results compare well with recent spectrally resolved experiments using synchrotron radiation which are also reported. As a novel XUV light source running at multi-kHz repetition rate and synchronized with laser pulses, high-order harmonic generation (HHG) opens new possibilities for extending these investigations to time-resolved studies at the femtosecond scale. [2008-047T] GAIN Porteur : Moustapha El Kurdi Thème 7 Enhanced photoluminescence of heavily n-doped germanium Article publié en 2009 Auteurs : Moustapha El Kurdi. Kociniewski, T. Ngo, TP. Boulmer, J. Debarre, D. Boucaud, P. Damlencourt, JF. Kermarrec, O. Bensahel, D Réf. : APPLIED PHYSICS LETTERS 97 (2009) 072512 We show that a significant enhancement of the direct band gap photoluminescence can be achieved at room temperature in bulk Ge and Ge-on-insulator heavily n-doped by gas immersion laser doping. The photoluminescence signal from bulk Ge and Ge-on-insulator increases with the donor concentration. An enhancement factor of 20 as compared to the undoped material is achieved near the 1550 nm wavelength for active dopant concentrations around 5x10(19) cm(-3). These results are supported by calculations of the Ge spontaneous emission spectrum taking into account the doping effect on the electron distribution in the direct and indirect conduction band valleys. 28/02/2013 25 PUBLICATIONS PROJETS 2008 Band structure and optical gain of tensile-strained germanium based on a 30 band k center dot p formalism Article publié en 2010 Auteurs : Moustapha El Kurdi. Fishman, G. Sauvage, S. Boucaud, P Réf. : JOURNAL OF APPLIED PHYSICS 107 (2010) 013710 We have investigated the band structure of tensile-strained germanium using a 30 band k center dot p formalism. This multiband formalism allows to simultaneously describe the valence and conduction bands, including the L, Delta, and Gamma valleys. We calculate the energy band variation as a function of strain and obtain that the crossover from indirect to direct band gap occurs for a tensile in-plane strain of 1.9%. The effective masses of density of states are deduced from the calculated conduction and valence band density of states. Significant deviations are observed as compared to the effective masses of density of states values of unstrained bulk germanium. We finally calculate the optical gain that can be achieved with tensile-strained bulk germanium. An optical gain larger than 3000 cm(-1) is predicted for a carrier density of 1x10(18) cm(-3) and a 3% in-plane biaxial strain. This optical gain is larger than the one of GaAs calculated with the same formalism and is much larger than the experimental free-carrier absorption losses. This gain should be sufficient to achieve lasing in these structures. Control of direct band gap emission of bulk germanium by mechanical tensile strain Article publié en 2010 Auteurs : Kurdi, M. Bertin, H. Martincic, E. de Kersauson, M. Fishman, G. Sauvage, S. Bosseboeuf, A. Boucaud, P Réf. : APPLIED PHYSICS LETTERS 96 (2010) 041909 We show that the recombination energy of the direct band gap photoluminescence (PL) of germanium can be controlled by an external mechanical stress. The stress is provided by an apparatus commonly used for bulge or blister test. An energy redshift up to 60 meV is demonstrated for the room temperature PL of a thin germanium membrane (125 nm wavelength shift from 1535 to 1660 nm). This PL shift is correlated with the in-plane tensile strain generated in the film. A biaxial tensile strain larger than 0.6% is achieved by this method. This mechanical strain allows to approach the direct band gap condition for germanium which is of tremendous importance to achieve lasing with this material. Direct and indirect band gap room temperature electroluminescence of Ge diodes Article publié en 2010 Auteurs : de Kersauson, M. Jakomin, R. Moustapha El Kurdi. Beaudoin, G. Zerounian, N. Aniel, F. Sauvage, S. Sagnes, I.Boucaud, P Réf. : JOURNAL OF APPLIED PHYSICS 108 (2010) 023105 Germanium is a promising material for electrically pumped light emitters integrated on silicon. In this work, we have investigated the room temperature electroluminescence of pure germanium diodes grown by metal organic chemical vapor deposition. The dependence of the optical response of the p-n diodes is studied as a function of the injected current. Both direct and indirect band gap recombinations are observed at room temperature around 1.6 and 1.8 mu m. The amplitude of the direct band gap recombination is equivalent to the one of the indirect band gap. (C) 2010 American Institute of Physics. [doi:10.1063/1.3462400] 28/02/2013 26 PUBLICATIONS PROJETS 2008 Control of tensile strain in germanium waveguides through silicon nitride layers Article publié en 2012 Auteurs : Ghrib A.; de Kersauson M.; El Kurdi M.; et al. Réf. : APPLIED PHYSICS LETTERS Volume: 100 10.1063/1.4718525 Published: MAY 14 2012 Issue: 20 Article Number: 201104 DOI: Germanium ridge waveguides can be tensilely strained using silicon nitride thin films as stressors. We show that the strain transfer in germanium depends on the width of the waveguides. Carrier population in the zone center Gamma valley can also be significantly increased when the ridges are oriented along the < 100 > direction. We demonstrate an uniaxial strain transfer up to 1% observed on the room temperature direct band gap photoluminescence of germanium. The results are supported by 30 band k . p modeling of the electronic structure and the finite element modeling of the strain field. (C) 2012 American Institute of Physics. [http://dx.doi.org.gate4.inist.fr/10.1063/1.4718525] [2008-048T] SPECTMAG Porteur : Jean-Christophe Girard Axe A Atomic structure of tip apex for spin-polarized scanning tunneling microscopy Article publié en 2008 Auteurs : Rodary, G; Jean-Christophe Girard ean-ChristopheGirard ; Largeau, L; David, C; Mauguin, O; Wang, ZZ Réf. : APPLIED PHYSICS LETTERS 98 (2011) 082505 We present a high resolution transmission electron microscopy study of a Cr-coated W tip apex prepared for spin-polarized scanning tunneling microscopy (SP-STM). The characterization of the tip apex structure has been done with atomic resolution. We show that the Cr film is epitaxially grown on W and presents a monocrystalline phase. The surface analysis of the apex reveals roughness which gives rise to structures that can be considered as nanotips. In spite of the monocrystalline structure of these nanotips, we show that their spin arrangement and resulting magnetization direction cannot be controlled. SP-STM measurements on a Cr/MgO(001) sample confirm this conclusion. (C) 2011 American Institute of Physics. 28/02/2013 27 PUBLICATIONS PROJETS 2008 [2008-051T] PHOTO-MAG Porteur : Isabelle Maurin Axe C Controlled growth of core@shell heterostructures based on Prussian blue analogues Article publié en 2011 Auteurs : Presle, M; Lemainque, J; Guigner, JM; Larquet, E; Isabelle Maurin; Boilot, JP; Gacoin, T Réf. : NEW JOURNAL OF CHEMISTRY 35 (6): 1296-1301 2011 This work aims to develop a controlled strategy for the growth of multifunctional core@shell nanoparticles based on Prussian blue analogues. We mainly focussed our attention on Rb0.45Co[Fe(CN)(6)](0.8)center dot 3H(2)[email protected][Cr(CN)(6)](0.7)center dot zH(2)O particles, which combine a photoswitchable (photomagnetic/-chromic) core with a ferromagnetic shell. The control of the chemical composition in the heterostructure is a key point to obtain the expected magnetic, optical and structural properties. We found that the removal of the unreacted species by washing after the growth of the primary particles led to an irreversible aggregation attributed to the desorption of stabilizing [Fe(CN)(6)]surface units. We showed that this difficulty could be overcome by washing the particles in a solution containing chromicyanide ions, which are precursors of the Rb0.2Ni[Cr(CN)(6)](0.7)center dot zH(2)O shell phase, thus avoiding a contamination of the shell. Both Xray diffraction and magnetic measurements confirmed that a controlled shell of the desired composition could be obtained this way. Magnetic Core-Shell Nanoparticles from Nanoscale-Induced Phase Segregation Article publié en 2011 Auteurs : Carenco Sophie; Le Goff Xavier F.; Shi Jing; et al. Réf. : CHEMISTRY OF MATERIALS Volume: 23 10.1021/cm200575g Published: APR 26 2011 Issue: 8 Pages: 2270-2277 DOI: Nanoscaling of the nickel phosphides profoundly alters their domains of stability. An original mechanism of "nanoscale-induced phase segregation" was uncovered in the present study: the appearance of two crystallized phases inside each single nanoparticle (here, Ni(2)P and Ni fcc), where the single-phase product (Ni(3)P) would have been preferred at the bulk scale. This behavior was obtained by reacting at low temperature (<220 degrees C) substoichiometric amounts of white phosphorus (P(4)) on well-defined monodisperse Ni nanoparticles in solution. Phosphorus insertion inside the Ni fcc nanoparticles triggers the crystallization of a Ni(2)P core surrounded by a Ni shell. The crystallization process was monitored by HRTEM, EFTEM, XRD, and SQUID analyses and revealed a direct transformation of Ni fcc to a core-shell structure without any other Ni(x)P(y) crystallized intermediate. This core-shell Ni-P system was tuned by adjusting the amount of P(4) added, providing tunable magnetic shells supported on monodisperse nanoparticles. 28/02/2013 28 PUBLICATIONS PROJETS 2008 Influence of Protected Annealing on the Magnetic Properties of gamma-Fe2O3 Nanoparticles Article publié en 2012 Auteurs : Vichery, Charlotte; Maurin, Isabelle; Bonville, Pierre; Boilot, Jean-Pierre; Gacoin, Thierry Réf. : JOURNAL OF PHYSICAL CHEMISTRY C Volume: 116 10.1021/jp305069a Published: AUG 2 2012 Issue: 30 Pages: 16311-16318 DOI: It is usually considered that nanoparticles synthesized by low-temperature routes present structural disorder, from extended defects to local rearrangements (e.g., vacancy ordering or inversion in spinel ferrites), that may severely impact their magnetic properties. In the present work, we have investigated the influence of postsynthesis thermal treatments on 7-nm-sized gamma-Fe2O3 nanoparticles prepared by room temperature coprecipitation of ferric and ferrous salts in alkaline medium, followed by the dispersion of the preformed particles in a sol gel silica binder. Such protected annealing in a refractory matrix prevents coalescence and growth, thus preserving the mean size and size distribution of the pristine particles. Structural characterizations show that heat treatments up to 1000 degrees C turned the raw grains into well-crystallized particles without transformation into hematite. This strategy thus allows accounting for the influence of structural rearrangements on magnetic properties at fixed particle size. For such 7 nm particles, postsynthesis heat treatments were found to the shell of misaligned spins at the surface. [2008-052T] ACOUSTIC Porteur : Sébastien Sauvage Thème 7 Homogeneous broadening of the S to P transition in InGaAs/GaAs quantum dots measured by infrared absorption imaging with nanoscale resolution Article publié en 2011 Auteurs : Sauvage S, Driss A, Reveret F; Boucaud, P Dazzi, A Prazeres, R Glotin, F Jean-Michel Ortega, JM Miard, A Halioua, Y Raineri, F Sagnes, I Lemaitre, A Réf. : PHYSICAL REVIEW B 83 (2011) 035302 Absorption of single InGaAs self-assembled quantum dots is spatially resolved in resonance with the S to P polaron transitions around lambda = 25 mu m wavelength. We show that the spatial resolution down to 50 nm (lambda/500) combined with the analysis of the absorption nanoscopy images provides a measurement of the homogeneous broadening at room temperature. The 2.5 +/- 1 meV measured S-P homogeneous broadening supports the calculated value accounting for acoustic phonon-induced decoherence. 28/02/2013 29 PUBLICATIONS PROJETS 2008 [2008-053T] SERPBIO Porteur : Niloufar Shafizadeh Thème 2 First observation in the gas phase of the ultrafast electronic relaxation pathways of the S-2 states of heme and hemin Article publié en 2010 Auteurs : Ha-Thi MH ; Niloufar Shafizadeh ; Poisson L ; Soep B Réf. : PHYSICAL CHEMISTRY CHEMICAL PHYSICS 12 (2010) 14985-14993 The time evolution of electronically excited heme (iron II protoporphyrin IX, [Fe-II PP]) and its associated salt hemin (iron III protoporphyrin IX chloride, [Fe-III PP-Cl]), has been investigated for the first time in the gas phase by femtosecond pump-probe spectroscopy. The porphyrins were excited at 400 nm in the S-2 state (Soret band) and their relaxation dynamics was probed by multiphoton ionization at 800 nm. This time evolution was compared with that of the excited state of zinc protoporphyrin IX [Zn PP] whose S2 excited state likely decays to the long lived S-1 state through a conical intersection, in less than 100 fs. Instead, for [Fe-II PP] and [Fe-III PPCl], the key relaxation step from S-2 is interpreted as an ultrafast charge transfer from the porphyrin excited orbital pi* to a vacant d orbital on the iron atom (ligand to metal charge transfer, LMCT). This intermediate LMCT state then relaxes to the ground state within 250 fs. Through this work a new, serendipitous, preparation step was found for Fe II porphyrins, in the gas phase. Strength of (NHS)-S-Hydrogen Bonds in Methionine Residues Revealed by Gas-Phase IR/UV Spectroscopy Article publié en 2012 Auteurs : Biswal Himansu S.; Gloaguen Eric; Loquais Yohan; et al. Réf. : JOURNAL OF PHYSICAL CHEMISTRY LETTERS Volume: 3 10.1021/jz300207k Published: MAR 15 2012 Issue: 6 Pages: 755-759 DOI: Despite of being ubiquitous in proteins, (NHbackboneS)-S-... hydrogen bonds linking the sulfur atom of methionine or cysteine to backbone NH groups remain poorly documented. Here, we report vibrationally resolved IR NH stretch spectra of two methionine-containing dipeptides (Ac-Phe-Met-NH2 and Ac-Met-PheNH2). The conformations observed for both molecules, assigned with the help of DFT-D quantum chemistry, provide spectroscopic evidence for the formation of (NHbackboneS)-S-... H-bonds, surprisingly strong enough to challenge the classical intrabackbone (NHO)-O-...=C H-bonds. The methionine side chain is found to fold locally, forming a H-bond with the neighboring amide groups (NH(i) or NH(i+1)). Comparison with protein data bank structural information shows that such a local folding is also common in proteins where it concerns 24% of the methionine residues that have a sulfur atom linked to a backbone NH group. This convergence between the strength of these (NHS)-S-... H-bonds and protein structural data illustrates their contribution to the stability of protein chains. 28/02/2013 30 PUBLICATIONS PROJETS 2008 [2008-053T] SERPEBIO & [2010-003T] COMOVA Porteur : Niloufar Shafizadeh Thème 2 Unraveling the Mechanisms of Nonradiative Deactivation in Model Peptides Following Photoexcitation of a Phenylalanine Residue Article publié en 2012 Auteurs : Malis, Momir; Loquais, Yohan; Gloaguen, Eric; Biswal, Himansu S.; Piuzzi, Francois; Tardivel, Benjamin; Brenner, Valerie; Broquier, Michel; Jouvet, Christophe; Mons, Michel; Doslic, Nada; Ljubic, Ivan Réf. : JOURNAL OF THE AMERICAN CHEMICAL SOCIETY Volume: 134 20351 DOI: 10.1021/ja3054942 Published: DEC 19 2012 Issue: 50 Pages: 20340- The mechanisms of nonradiative deactivation of a phenylalanine residue after near-UV photoexcitation have been investigated in an isolated peptide chain model (N-acetylphenylalaninylamide, NAPA) both experimentally and theoretically. Lifetime measurements at the origin of the first pi pi* state of jet-cooled NAPA molecules have shown that (i) among the three most stable conformers of the molecule, the folded conformer NAPA B is similar to 50-times shorter lived than the extended major conformer NAPA A and (ii) this lifetime is virtually insensitive to deuteration at the NH2 and NH sites. Concurrent time-dependent density functional theory (TDDFT) based nonadiabatic dynamics simulations in the full dimensionality, carried out for the NAPA B conformer, provided direct insights on novel classes of ultrafast deactivation mechanisms, proceeding through several conical intersections and leading in fine to the ground state. These mechanisms are found to be triggered either (i) by a stretch of the NpheH bond, which leads to an H-transfer to the ring, or (ii) by specific backbone amide distortions. The potential energy surfaces of the NAPA conformers along these critical pathways have been characterized more accurately using the coupled cluster doubles (CC2) method and shown to exhibit barriers that can be overcome with moderate excess energies. These results analyzed in the light of the experimental findings enabled us to assign the short lifetime of NAPA B conformer to a number of easily accessible exit channels from the initial pi pi* surface, most importantly the one involving a transfer of electronic excitation to an n pi* surface, induced by distortions of the backbone peptide bond. [2008-054T] SYMTCOB Porteur : H. Alloul Thème 4 Growth and characterisation of Li(x)CoO(2) single crystals Article publié en 2011 Auteurs : L. Pinsard-Gaudart,V.C. Ciomaga, O. Dragos, R. Guillot, N. Dragoe Réf. : JOURNAL OF CRYSTAL GROWTH Volume: 334 Issue: 1 DOI: 10.1016/j.jcrysgro.2011.07.024 Published: NOV 1 2011 28/02/2013 31 PUBLICATIONS PROJETS 2008 Centimetre-size single crystals of LiCoO(2) were successfully grown using a floating-zone method associated with an image furnace. A high-pressure oxygen atmosphere and a relatively small growth speed were found necessary to prevent the formation of impurity phases in the grown crystal. A single crystal with a reduced amount of lithium was obtained by means of the chemical de-lithiation process using as grown LiCoO(2) single crystal as the starting material. Growth conditions together with magnetic and structural properties of these crystals are discussed here. (C) 2011 Elsevier B.V. All rights reserved. Na-23 NMR study of sodium order in NaxCoO2 with 22 K Neel temperature Article publié en 2012 Auteurs : Alloul H.; Mukhamedshin I. R.; Dooglav A. V.; et al. Réf. : PHYSICAL REVIEW B Volume: 85 Issue: 13 10.1103/PhysRevB.85.134433 Published: APR 20 2012 Article Number: 134433 DOI: Pas d'abstract [2008-055T] GRAMINE Porteur : Sophie Noël Axe C Conductive-probe AFM characterization of graphene sheets bonded to gold surfaces Article publié en 2012 Auteurs : Hauquier, Fanny; Alamarguy, David; Viel, Pascal; Noel, Sophie; Filoramo, Arianna; Huc, Vincent; Houze, Frederic; Palacin, Serge Réf. : APPLIED SURFACE SCIENCE, 258 (7):2920-2926; 10.1016/j.apsusc.2011.10.152 JAN 15 2012 Conducting probe atomic force microscopy (CP-AFM) has been used to perform mechanical and electrical experiments on graphene layers bonded to polyaminophenylene (PAP) films grafted on gold substrates. This technique is a new approach for the characterization of graphene sheets and represents a complementary tool to Raman spectroscopy. The combination of friction and electrical imaging reveals that different stacked graphene sheets have been successfully distinguished from each other and from the underlying PAP films. Lateral force microscopy has shown that the friction is greatly reduced on graphene sheets in comparison with the organic coating. The electrical resistance images show very different local conduction properties which can be linked to the number of underlying graphene sheets. The resistance decreases very slowly when the normal load increases. Current-voltage curves display characteristics of metal-molecule-metal junctions. (C) 2011 Elsevier B.V. All rights reserved. 28/02/2013 32 PUBLICATIONS PROJETS 2008 [2008-056T] FLAG Porteur : Bertrand Poumellec Thème 7 Anatomy of a femtosecond laser processed silica waveguide [Invited] Article publié en 2011 Auteurs : Canning J.; Lancry M.; Cook K.; et al. Réf. : OPTICAL MATERIALS EXPRESS Volume: 1 Issue: 5 Pages: 998-1008 Published: SEP 1 2011 Waveguides are inscribed through densification of the surrounding region of a damage induced channel created by femtosecond irradiation within silica. Single mode propagation at 1.5 mu m is obtained below the damage region whilst at shorter wavelengths guidance is only observed away on either side of the region. The quasiperiodic nanostructure that is induced can explain the mode profile elongation observed with polarised light at 45. The origin of this guidance area is explored using SEM analysis, which reveals nanoporous regions within laser track structure above and below the densified region where 1.5 mu m propagates. Shorter wavelength light is not supported in this area. (C) 2011 Optical Society of America Dependence of the femtosecond laser refractive index change thresholds on the chemical composition of doped-silica glasses Article publié en 2011 Auteurs : Lancry, M; Poumellec, B; Chahid-Erraji, A; Beresna, M; Kazansky, PG Réf. : OPTICAL MATERIALS EXPRESS, 1 (4):711-723; AUG 1 2011 The refractive index changes in doped silica are investigated. We observed that the permanent isotropic index change threshold (T1) is not significantly dependent on the doping. We show that strong birefringence (permanent linear birefringence) exists in doped silica but its threshold (T2) exhibits significant dependence on the used dopants. In our conditions, comparing with silica (0.31 mu J/pulse here), for 1.5 at% Ge-doped silica the T2 threshold is smaller (0.14 +/- 0.05 mu J/pulse). For a silica doped with 0.3 at% of fluorine, T2 is close to 1.20 +/- 0.05 mu J/pulse. An interpretation is given not only about threshold variation but also about RIC for energies beyond. It is based on the overcoming of relaxation time in the volume interaction. (C) 2011 Optical Society of America Modification thresholds in femtosecond laser processing of pure silica: review of dependencies on laser parameters [Invited] Article publié en 2011 Auteurs : Poumellec, B; Lancry, M; Chahid-Erraji, A; Kazansky, PG Réf. : OPTICAL MATERIALS EXPRESS, 1 (4):766-782; AUG 1 2011 This review allows better defining the domains of macroscopic effects produced by the femtosecond laser irradiation in pure silica according to the laser parameters. (C) 2011 Optical Society of America 28/02/2013 33 PUBLICATIONS PROJETS 2008 Time-resolved plasma measurements in Ge-doped silica exposed to infrared femtosecond laser Article publié en 2011 Auteurs : Lancry M.; Groothoff N.; Poumellec B.; et al Réf. : PHYSICAL REVIEW B Volume: 84 Issue: 24 10.1103/PhysRevB.84.245103 Published: DEC 8 2011 Article Number: 245103 DOI: Using a time-resolved interferometric technique, we study the laser-induced carrier-trapping dynamics in SiO(2) and Ge-doped SiO(2). The fast trapping of electrons in the band gap is associated with the formation of selftrapped excitons (STE). The STE trapping is doping dependent in SiO(2). The mean trapping time of electrons excited in the conduction band was found to be significantly lower in Ge-doped silica (75 +/- 5 fs) when compared to pure silica (155 +/- 5 fs). At our concentration level, this indicates that the plasma properties are determined by the presence of easily ionizable states such as the presence of Ge atoms in the glass network. Therefore, we suggest that in Ge-doped silica there exist an additional trapping pathway that leads to a significantly faster excitons trapping and a higher plasma density when compared to undoped silica. Gold Nanoparticles Reshaped by Ultrafast Laser Irradiation Inside a Silica-Based Glass, Studied Through Optical Properties Article publié en 2012 Auteurs : Fan Chaxing; Poumellec Bertrand; Zeng Huidan; et al. Réf. : JOURNAL OF PHYSICAL CHEMISTRY C Volume: 116 10.1021/jp203408y Published: FEB 2 2012 Issue: 4 Pages: 2647-2655 DOI: Quasi-spherical or quasi-rod gold nanoparticles with an average diameter of 3.8 nm are randomly precipitated in a silica-based glass by a heat-treatment method. After ultrafast laser irradiation at 400 and 620 nm, optical absorption, birefringence, and dichroism measurements are performed to investigate the modification of gold nanoparticles shape. Theoretical simulations have been carried out to interpret the experimental results. We suggest that a small fraction of gold nanospheres are transformed mainly into nanodisks but also into nanorods oriented along the laser polarization for both fs laser wavelength. Absorption simulation suggests that they have an aspect ratio of 1.8 and 0.5, respectively, for fs laser irradiation at 400 nm. For 620 nm, the aspect ratio of the nanorods increases and the one of the nanodisks decreases. In such a way, we demonstrate that reshaping of gold nanoparticles, i.e. a property that was previously found for silver nanoparticles in multicomponent glass is also possible. By imaging the distribution of the birefringence according to the probe wavelength, we show that nanopartides are aligned into nanorods mainly out of irradiated volume and into nanopellets mainly in the irradiated volume. Oriented creation of anisotropic defects by IR femtosecond laser scanning in silica Article publié en 2012 Auteurs : Lancry, M.; Poumellec, B.; Desmarchelier, R.; Bourguignon, B. Réf. : OPTICAL MATERIALS EXPRESS Volume: 2 2012 Issue: 12 Pages: 1809-1821 Published: DEC 1 Irradiation of non-luminescent silica with polarized IR femtosecond laser light produced a significant amount of luminescent defects. We have investigated the properties of luminescence produced by the defects using UVVUV excitation experiment depending on the relative orientation of the laser polarization and its scanning direction. Silicon Oxygen Deficient Center (SiODC) is identified. SiODC related luminescence is much stronger 28/02/2013 34 PUBLICATIONS PROJETS 2008 when the excitation polarization is parallel to the sample scanning direction and moved at low velocity, regardless of the writing polarization direction. This indicates that the creation of this anisotropic defect is oriented by the movement of the femtosecond laser beam. (C)2012 Optical Society of America Three-dimensional photoprecipitation of oriented LiNbO3-like crystals in silica-based glass with femtosecond laser irradiation Article publié en 2012 Auteurs : Fan, Chaxing; Poumellec, Bertrand; Lancry, Matthieu; He, Xuan; Zeng, Huidan; ErrajiChahid, Abdel; Liu, Qiming; Chen, Guorong Réf. : OPTICS LETTERS Volume: 37 Issue: 14 Pages: 2955-2957 Published: JUL 15 2012 We demonstrate crystals (LiNbO3-like) that were space-selectively nucleated and grown in the bulk of silicabased glass by femtosecond laser irradiation at a high repetition rate (typ. 300 kHz). Oriented crystals with their polar axis mostly aligned with or perpendicular to the laser scanning direction have been fabricated by manipulation of the temperature gradient in adjusting the laser parameters. The mechanism for the orientation of femtosecond laser-induced crystallization is briefly discussed. (C) 2012 Optical Society of America [2008-057T] PAO Porteur : Jean-Jacques Greffet Thème 7 Dielectric gratings for wide-angle, broadband absorption by thin film photovoltaic cells Article publié en 2010 Auteurs : Laroche M ; Greffet JJ; R. Esteban Réf. : APPLIED PHYSICS LETTERS 97 (2010) 221111 Optical management is essential to increase absorption in thin photovoltaic cells. In this article, full electromagnetic simulations show that a back mirror and a one-dimensional front SiC sawtooth grating of similar to 1 mu m dimensions can significantly increase absorption in a thin layer under light concentration. A 50 nm thick GaSb active layer in the described configuration absorbs similar to 66% of the incident solar photons above the band gap for a concentration equivalent to a numerical aperture NA=1/root 2. This absorption represents a similar to 76% or 26% increase over the same structure but with the grating removed or substituted by an ideal antireflection coating, respectively. (C) 2010 American Institute of Physics. [doi: 10.1063/1.3512898] Optical Patch Antennas for Single Photon Emission Using Surface Plasmon Resonances Article publié en 2010 Auteurs : Esteban, R. Teperik, TV. Jean-Jacques Greffet Réf. : PHYSICAL REVIEW LETTERS 104 (2010) 026802 28/02/2013 35 PUBLICATIONS PROJETS 2008 Single photon sources can greatly benefit from specially designed structures that modify the properties of the photon emitter. Dielectric cavities are often discussed, but they require a compromise between the spectral width and Purcell factor. In this Letter, we introduce plasmonic cavities as promising alternatives. We first study how the emitter couples with the modes of such structures. We then show how a patch antenna configuration simultaneously presents a large Purcell factor, collection efficiency, and spectral width. Experimental study of hot spots in gold/glass nanocomposite films by photoemission electron microscopy Article publié en 2012 Auteurs : Awada, C.; Barbillon, G.; Charra, F.; Douillard, L.; Greffet, J. -J. Réf. : PHYSICAL REVIEW B, 85 (4):10.1103/PhysRevB.85.045438 JAN 24 2012 In this paper, an experimental study of hot spots in gold/dielectric films using photoemission electron microscopy is reported. This technique allows a characterization of the statistical optical properties with unprecedented accuracy in the 800- to 1040-nm range. Theoretical predictions of the scaling theory on the number and intensity wavelength dependences of hot spots in the near-infrared are confirmed. Statistical properties of the intensity distribution, spectral behavior, and spatial localization of the hot spots are reported. Nanoscale magnetic field mapping with a single spin scanning probe magnetometer Article publié en 2012 Auteurs : Rondin L.; Tetienne J. -P.; Spinicelli P.; et al. Réf. : APPLIED PHYSICS LETTERS Volume: 100 10.1063/1.3703128 Published: APR 9 2012 Issue: 15 Article Number: 153118 DOI: We demonstrate quantitative magnetic field mapping with nanoscale resolution, by applying a lock-in technique on the electron spin resonance frequency of a single nitrogen-vacancy defect placed at the apex of an atomic force microscope tip. In addition, we report an all-optical magnetic imaging technique which is sensitive to large off-axis magnetic fields, thus extending the operation range of diamond-based magnetometry. Both techniques are illustrated by using a magnetic hard disk as a test sample. Owing to the non-perturbing and quantitative nature of the magnetic probe, this work should open up numerous perspectives in nanomagnetism and spintronics. (C) 2012 American Institute of Physics. [http://dx.doi. org/10.1063/1.3703128] [2008-058T] FemtoARPES Porteur : Marino Marsi Thème 4 Coherent Phonon Coupling to Individual Bloch States in Photoexcited Bismuth Article publié en 2012 Auteurs : Papalazarou, E.; Faure, J.; Mauchain, J.; Marsi, M.; Taleb-Ibrahimi, A.; Reshetnyak, I.; van Roekeghem, A.; Timrov, I.; Vast, N.; Arnaud, B.; Perfetti, L. 28/02/2013 36 PUBLICATIONS PROJETS 2008 Réf. : PHYSICAL REVIEW LETTERS Volume: 108 Issue: 25 10.1103/PhysRevLett.108.256808 Published: JUN 20 2012 Article Number: 256808 DOI: We investigate the temporal evolution of the electronic states at the bismuth (111) surface by means of time- and angle-resolved photoelectron spectroscopy. The binding energy of bulklike bands oscillates with the frequency of the A(1g) phonon mode, whereas surface states are insensitive to the coherent displacement of the lattice. A strong dependence of the oscillation amplitude on the electronic wave vector is correctly reproduced by ab initio calculations of electron-phonon coupling. Besides these oscillations, all the electronic states also display a photoinduced shift towards higher binding energy whose dynamics follows the evolution of the electronic temperature. Giant Anisotropy of Spin-Orbit Splitting at the Bismuth Surface Article publié en 2012 Auteurs : Ohtsubo, Y.; Mauchain, J.; Faure, J.; Papalazarou, E.; Marsi, M.; Le Fevre, P.; Bertran, F.; Taleb-Ibrahimi, A.; Perfetti, L. Réf. : PHYSICAL REVIEW LETTERS Volume: 109 Issue: 22 10.1103/PhysRevLett.109.226404 Published: NOV 27 2012 Article Number: 226404 DOI: We investigate the bismuth (111) surface by means of time and angle resolved photoelectron spectroscopy. The parallel detection of the surface states below and above the Fermi level reveals a giant anisotropy of the spinorbit spitting. These strong deviations from the Rashba-like coupling cannot be treated in k.p perturbation theory. Instead, first principles calculations could accurately reproduce the experimental dispersion of the electronic states. Our analysis shows that the giant anisotropy of the spin-orbit splitting is due to a large out-of plane buckling of the spin and orbital texture. Ultrafast Surface Carrier Dynamics in the Topological Insulator Bi2Te3 Article publié en 2012 Auteurs : Hajlaoui, M.; Papalazarou, E.; Mauchain, J.; Lantz, G.; Moisan, N.; Boschetto, D.; Jiang, Z.; Miotkowski, I.; Chen, Y. P.; Taleb-Ibrahimi, A.; Perfetti, L.; Marsi, M. Réf. : NANO LETTERS Volume: 12 Issue: 7 Pages: 3532-3536 DOI: 10.1021/nl301035x Published: JUL 2012 We discuss the ultrafast evolution of the surface electronic structure of the topological insulator Bi2Te3 following a femtosecond laser excitation. Using time and angle-resolved photoelectron spectroscopy, we provide a direct real-time visualization of the transient carrier population of both the surface states and the bulk conduction band. We find that the thermalization of the surface states is initially determined by interband scattering from the bulk conduction band, lasting for about 0.5 ps; subsequently, few picoseconds are necessary for the Dirac cone non-equilibrium electrons to recover a Fermi-Dirac distribution, while their relaxation extends over more than 10 ps. The surface sensitivity of our measurements makes it possible to estimate the range of the bulk-surface interband scattering channel, indicating that the process is effective over a distance of 5 nm or less. This establishes a correlation between the nanoscale thickness of the bulk charge reservoir and the evolution of the ultrafast carrier dynamics in the surface Dirac cone. 28/02/2013 37 PUBLICATIONS PROJETS 2008 Ultrafast filling of an electronic pseudogap in an incommensurate crystal Article publié en 2013 Auteurs : Brouet, V.; Mauchain, J.; Papalazarou, E.; Faure, J.; Marsi, M.; Lin, P. H.; Taleb-Ibrahimi, A.; Le Fevre, P.; Bertran, F.; Cario, L.; Janod, E.; Corraze, B.; Phuoc, V. Ta; Perfetti, L. Réf. : PHYSICAL REVIEW B Volume: 87 Issue: 4 10.1103/PhysRevB.87.041106 Published: JAN 28 2013 Article Number: 041106 DOI: We investigate the quasiperiodic crystal (LaS)(1.196)VS2 by angle and time resolved photoemission spectroscopy. The dispersion of electronic states is in qualitative agreement with the band structure calculated for the VS2 slab without incommensurate distortion. Nonetheless, the spectra display a temperature dependent pseudogap instead of quasiparticle crossing. The sudden photoexcitation at 50 K induces a partial filling of the electronic pseudogap within less than 80 fs. The electronic energy flows into the lattice modes on a comparable time scale. We attribute this surprisingly short time scale to a very strong electron-phonon coupling to the incommensurate distortion. This result sheds light on the electronic localization arising in aperiodic structures and quasicrystals. DOI: 10.1103/PhysRevB.87.041106 [2008-060T] MeMoFri Porteur : Liliane Leger Thème 3 Contact Angle and Contact Angle Hysteresis Measurements Using the Capillary Bridge Technique Article publié en 2009 Auteurs : Restagno, F. Poulard, C. Cohen, C. Vagharchakian, L. Leger, L Réf. : LANGMUIR 25 (2009) 11188-11196 A new experimental technique is proposed to easily measure both advancing and receding contact angles of a liquid on a solid surface, with unprecedented accuracy. The technique is based on the analysis of the evolution of a capillary bridge formed between a liquid bath and a solid surface (which needs to be spherical) when the distance between the surface and the liquid bath is slowly varied. The feasibility of the technique is demonstrated using a low-energy perfluorinated Surface with two different test liquids (water and hexadecane). A detailed description of both experimental procedures and computational modeling are given, allowing one to determine contact angle Values. It is shown that the origin of the high accuracy of this technique relies on the fact that the con tact angles are automatically averaged over the whole periphery of the contact. This method appears to be particularly adapted to the characterization Of surfaces with very low contact angle hysteresis. Incidence of the molecular organization on friction at soft polymer interfaces Article publié en 2011 Auteurs : Cohen, Celine; Restagno, Frederic; Poulard, Christophe; Leger, Liliane 28/02/2013 38 PUBLICATIONS PROJETS 2008 Réf. : SOFT MATTER 7 (18): 8535-8541 10.1039/c1sm05874f 2011 Polymer molecules strongly anchored to a solid substrate and interdigitated into bulk crosslinked elastomer have been shown recently to efficiently promote adhesion and friction between substrate and elastomer. Concerning friction, the regime of low surface coverage in surface anchored chains has been fully and quantitatively accounted for by the pull off mechanisms, where individual chains are dynamically extracted from the elastomer. Then, the stretching energy of these chains dominates the friction losses. We focus here on the dense surface coverage regime. We present systematic experiments performed on the polydimethylsiloxane (PDMS) - silica system, and determine molecular weight and sliding velocity dependences of the friction stress. We show that the friction is dominated by the shear thinning of the grafted layer confined between the elastomer and the substrate, and responding to the shear solicitation like a melt, but with very long relaxation times. We also show that the friction stress appears highly sensitive to the molecular organization inside the surface anchored polymer layer, comparing end grafted and strongly adsorbed layers having otherwise the same molecular characteristics (molecular weight of the chains, and thickness of the surface anchored layer). Synthesis of well-defined poly(dimethylsiloxane) telechelics having nitrobenzoxadiazole fluorescent chain-ends via thiol-ene coupling Article publié en 2012 Auteurs : Cohen Celine; Damiron Denis; Ben Dkhil Sadok; et al. Réf. : JOURNAL OF POLYMER SCIENCE PART A-POLYMER CHEMISTRY Volume: 50 Issue: 9 Pages: 1827-1833 DOI: 10.1002/pola.25952 Published: MAY 1 2012 Well-defined PDMS telechelics having nitrobenzoxadiazole (NBD) fluorescent probes covalently attached at both chain-ends were prepared in two steps and a series of fractionation procedures starting from commercially available divinyl-terminated PDMS having a broad molar mass dispersity. First, thiol-ene coupling between 6mercapto-1-hexanol and vinyl chain-ends allowed the formation of dihydroxy-terminated PDMS telechelics through the formation of a thioether linkage. The resulting material was then sequentially fractionated using dichloromethane/methanol mixtures to afford several well-defined dihydroxy-terminated PDMS fractions having sharp distributions of molar masses (Mn = 99.5158 kDa and D < 1.2). The NBD fluorescent probes were then attached at both chain-ends by N,N'-dicyclohexylcarbodiimide/4-(dimethylamino)pyridine esterification coupling between the hydroxyl groups and 6-(7-nitrobenzofurazan-4-ylamino)hexanoic acid. The resulting fluorescent PDMS telechelics were characterized by SEC, 1H NMR, UVvisible, and fluorescence spectroscopies. These materials are suitable probes to investigate the dynamics of polymer chains in bulk or at interfaces by the fringe pattern fluorescent recovery after photobleaching technique. (C) 2012 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem, 2012 Wetting and Dewetting Transition: An Efficient Toolbox for Characterizing Low-Energy Surfaces Article publié en 2010 Auteurs : Cohen, C. Restagno, F. Poulard, C. Leger, L. Réf. : LANGMUIR 26 (2010) 15345-15349 The capillary bridge formed between a solid spherical surface and an infinite liquid bath is an efficient technique for characterizing the adhesion property of a solid surface. When the solid surface is pulled out of the liquid at a sufficiently high velocity, a thin liquid film is deposited on the solid and drains more slowly than the central capillary bridge. The retraction kinetics of this "pancake" and the critical velocity above which it appears are studied as a function of the viscosity of the liquid or the wettability of the solids. The dynamics of the liquid film follows the classical law of dynamic dewetting. This makes the capillary bridge test, used in the dynamical regime, a very efficient tool for discriminating between antiadhesive coatings. 28/02/2013 39 PUBLICATIONS PROJETS 2008 [2008-061T] MINIATOM Porteur : Philippe Bouyer Thème 1 Light-pulse atom interferometry in microgravity Article publié en 2009 Auteurs : Stern, G. Battelier, B. Geiger, R. Varoquaux, G. Villing, A. Moron, F. Carraz, O. Zahzam, N. Bidel, Y. Chaibi, W. Dos Santos, FP. Bresson, A. Landragin, A. Bouyer, P Réf. : EUROPEAN PHYSICAL JOURNAL D 57 (2009) 87-94 We describe the operation of a light pulse interferometer using cold Rb-87 atoms in reduced gravity. Using a series of two Raman transitions induced by light pulses, we have obtained Ramsey fringes in the low gravity environment achieved during parabolic flights. With our compact apparatus, we have operated in a regime which is not accessible on ground. In the much lower gravity environment and lower vibration level of a satellite, our cold atom interferometer could measure accelerations with a sensitivity orders of magnitude better than the best ground based accelerometers and close to proven spaced-based ones. Frequency doubled 1534nm laser system for potassium laser cooling Article publié en 2010 Auteurs : Stern G, Allard B, Robert-De-Saint-Vincent M, Brantut JP , Battelier B, Bourdel T, Bouyer P Réf. : APPLIED OPTICS 49 (2010) We demonstrate a compact laser source suitable for trapping and cooling potassium. By frequency doubling a fiber laser diode at 1534nm in a waveguide, we produce 767nm laser light. A current modulation of the diode allows us to generate the two required frequencies for cooling in a simple and robust apparatus. We successfully used this laser source to trap K-39. (c) 2010 Optical Society of America [2008-062T] DYNANEX Porteur : Lionel Poisson Thème 2 Photoionization of 2-pyridone and 2-hydroxypyridine Article publié en 2010 Auteurs : Poully, JC. Schermann, JP. Nieuwjaer, N. Lecomte, F. Gregoire, G. Desfrancois, C. Garcia, GA. Nahon, L. Nandi, D. Poisson, L. Hochlaf, M Réf. : PHYSICAL CHEMISTRY CHEMICAL PHYSICS 12 (2010) 3566-3572 28/02/2013 40 PUBLICATIONS PROJETS 2008 We studied the photoionization of 2-pyridone and its tautomer, 2-hydroxypyridine by means of VUV synchrotron radiation coupled to a velocity map imaging electron/ion coincidence spectrometer. The photoionization efficiency (PIE) spectrum is composed of steps. The state energies of the [2-pyridone](+) cation in the (X) over tilde ground and (A) over tilde excited electronic states, as well as of the [2-hydroxypyridine](+) cation in the electronic ground state, are determined. The slow photoelectron spectra (SPES) are dominated by the 0(0)(0) transitions to the corresponding electronic states together with several weaker bands corresponding to the population of the pure or combination vibrational bands of the cations. These vibrationally-resolved spectra compare very well with state-of-the-art calculations. Close to the ionization thresholds, the photoionization of these molecules is found to be mainly dominated by a direct process whereas the indirect route (autoionization) may contribute at higher energies. A two-step ICT process for solvatochromic betaine pyridinium revealed by ultrafast spectroscopy, multivariate curve resolution, and TDDFT calculations Article publié en 2012 Auteurs : Aloise Stephane; Pawlowska Zuzanna; Ruckebusch Cyril; et al. Réf. : PHYSICAL CHEMISTRY CHEMICAL PHYSICS Volume: 14 10.1039/c2cp22254j Published: 2012 Issue: 6 Pages: 1945-1956 DOI: This work deals with the photophysics of a pyridinium betaine, 2-pyridin-1-yl-1H-benzimidazole (SBPa), based on a combination of steady-state, femtosecond photoionization (gas phase) and femtosecond transient absorption (solution) spectroscopic measurements, supported by (LR)-PCM-(TD)DFT calculations. Preliminary and new electrochemical results have revealed a strongly negative solvatochromic charge transfer (CT) absorption due to a S-0 -> S-2 vertical transition and a weakly-solvatochromic emission due to S-1 -> S-0 transition. Advanced TDDFT optimizations of the Franck-Condon states S-2(FC) and S-1(FC) led to two additional CT levels with planar geometry, S-2(CT) and S-1(CT), respectively, allowing prediction of a two-step photoinduced ICT process, i.e., S-0 -> S-2(FC) and S-2(CT) -> S-1(CT), separated by a S-2(FC) -> S-2(CT) back charge transfer relaxation. While the pyridinium ring is the acceptor group in both steps, two different donor groups, the benzene ring and the imidazole bridge, are involved in the excitation and internal conversion processes, respectively. Femtosecond transient absorption experiments supported by MCR-ALS decomposition confirmed indeed the contribution of two distinct CT states in the photophysics of SBPa: following excitation to the S2(CT) state, ultrafast production of the emissive S-1 state (the only channel observable in the gas phase) was observed to occur in competition with a further ICT process toward the S-1(CT) state, with a time constant ranging from 300 fs to 20 ps depending on the solvent. While in aprotic media this ICT process was found to be purely solvent controlled (double polarity and viscosity dependency), in protic solvents, the influence of the hydrogen bond network has to be taken into account. Comparison with data obtained for a pre-twisted SBPa analogue led us to exclude the presence of any large-amplitude geometrical change during ICT. Analyzing the solvent dependency using the power law approach, we concluded that the S-1(CT) state decays essentially through IC in the 3-40 ps time range whereas the emissive S-1 state decays within 130-260 ps via IC, ISC and fluorescence. Femtosecond dynamics of cyclopropenylidene, c-C3H2 Article publié en 2012 Auteurs : Hemberger Patrick; Koehler Juliane; Fischer Ingo; et al. Réf. : PHYSICAL CHEMISTRY CHEMICAL PHYSICS Volume: 14 10.1039/c2cp23728h Published: 2012 Issue: 18 Pages: 6173-6178 DOI: The photophysics of the B B-1(1) state of isolated cyclopropenylidene, c-C3H2, has been studied by femtosecond time-resolved photoionisation and photoelectron spectroscopy. The carbene was produced by flash 28/02/2013 41 PUBLICATIONS PROJETS 2008 pyrolysis of 3-chlorocycloprop-1-ene. The bands at 266.9 nm and 264.6 nm have been investigated. The excited state deactivates in a two step process. The first time constant of less than 50 fs corresponds most likely to a nonradiative transition to the A-state, the second one on the order of 200 fs describes the internal conversion to the electronic ground state. The data are compared to those measured for the chlorinated carbene c-C3HCl. In the photoelectron spectrum of c-C3H2 resonances were observed which can be assigned to members of a Rydberg dseries. [2008-063T] SAMNANO Porteur : Vladimir Esaulov Thème 2 UPS, XPS, and NEXAFS Study of Self-Assembly of Standing 1,4Benzenedimethanethiol SAMs on Gold Article publié en 2011 Auteurs : Pasquali, L; Terzi, F; Seeber, R; Nannarone, S; Datta, D; Dablemont, C; Hamoudi, H; Canepa, M; Esaulov, VA Réf. : LANGMUIR 27 (8): 4713-4720 APR 19 2011 We report a study of the self-assembly of 1,4-benzenedimethanethiol monolayers on gold formed in n-hexane solution held at 60 degrees C for 30 mm and in dark conditions. The valence band characteristics, the thickness of the layer, and the orientation of the molecules were analyzed at a synchrotron using high resolution photoelectron spectroscopy and near edge X-ray adsorption spectroscopy. These measurements unambiguously attest the formation of a single layer with molecules arranged in the upright position and presenting a free -SH group at the outer interface. Near edge X-ray absorption fine structure (NEXAFS) measurements suggest that the molecular axis is oriented at 24 degrees with respect to the surface normal. In addition, valence band features could be successfully associated to specific molecular orbital contributions thanks to the comparison with theoretically calculated density of states projected on the different molecular units. [2008-064T] THERMETG Porteur : Bérengère Dubrulle Thème 3 Relevance of visco-plastic theory in a multi-directional inhomogeneous granular flow Article publié en 2009 Auteurs : Cortet, PP. Bonamy, D. Daviaud, F. Olivier Dauchot. Bérengère Dubrulle. Renouf, M Réf. : EPL 88 (2009) 30009 28/02/2013 42 PUBLICATIONS PROJETS 2008 We confront a recent visco-plastic description of dense granular flows (Jop P. et al., Nature, 441 (2006) 727) with multi-directional inhomogeneous steady flows observed in non-smooth contact dynamics simulations of 2D half-filled rotating drums. Special attention is paid to check separately the two underlying fundamental statements into which the considered theory can be recast, namely i) a single relation between the invariants of stress and strain rate tensors and ii) the alignment between these tensors. Interestingly, the first prediction is fairly well verified over more than four decades of small strain rate, from the surface rapid flow to the quasistatic creep phase, where it is usually believed to fail because of jamming. On the other hand, the alignment between stress and strain rate tensors is shown to fail over the whole flow, what yields an apparent violation of the visco-plastic rheology when applied without care. In the quasi-static phase, the particularly large misalignment is conjectured to be related to transient dilatancy effects. Copyright (C) EPLA, 2009 Experimental Evidence of a Phase Transition in a Closed Turbulent Flow Article publié en 2010 Auteurs : Cortet PP ; Chiffaudel A ; Daviaud F ; Bérengère Dubrulle Réf. : PHYSICAL REVIEW LETTERS 105 (2010) 205418 We experimentally study the susceptibility to symmetry breaking of a closed turbulent von Karman swirling flow from Re 150 to Re similar or equal to 10(6). We report a divergence of this susceptibility at an intermediate Reynolds number Re = Re-chi similar or equal to 90 000 which gives experimental evidence that such a highly space and time fluctuating system can undergo a "phase transition.'' This transition is furthermore associated with a peak in the amplitude of fluctuations of the instantaneous flow symmetry corresponding to intermittencies between spontaneously symmetry breaking metastable states. Susceptibility divergence, phase transition and multistability of a highly turbulent closed flow Article publié en 2011 Auteurs : Cortet, PP; Herbert, E; Chiffaudel, A; Daviaud, F; Dubrulle, B; Padilla, V Réf. : JOURNAL OF STATISTICAL MECHANICS-THEORY AND EXPERIMENT 5468/2011/07/P07012 JUL 2011 10.1088/1742- Using time series of stereoscopic particle image velocimetry data, we study the response of a turbulent von Karman swirling flow to a continuous breaking of its forcing symmetry. Experiments are carried over a wide Reynolds number range, from the laminar regime at Re = 10(2) to the highly turbulent regime near Re = 10(6). We show that the flow symmetry can be quantitatively characterized by two scalars, the global angular momentum I and the mixing layer altitude z(s), which are shown to be statistically equivalent. Furthermore, we report that the flow response to small forcing asymmetry is linear, with a slope depending on the Reynolds number: this response coefficient increases non-monotonically from small to large Reynolds number and presents a divergence at a critical Reynolds number Re(c) = 40 000 +/- 5000. This divergence coincides with a change in the statistical properties of the instantaneous flow symmetry I(t): its pdf changes from Gaussian to non-Gaussian with multiple maxima, revealing metastable non-symmetrical states. For symmetric forcing, a peak of fluctuations of I(t) is also observed at Re(c): these fluctuations correspond to time intermittencies between metastable states of the flow which, contrary to the very-long-time-averaged mean flow, spontaneously and dynamically break the system symmetry. We show that these observations can be interpreted in terms of divergence of the susceptibility to symmetry breaking, revealing the existence ofa phase transition. An analogy with the ferromagnetic-paramagnetic transition in solid-state physics is presented and discussed. 28/02/2013 43 PUBLICATIONS PROJETS 2008 [2008-065T] Glasdespin Porteur : Isabelle Mirebeau Thème 4 Magnetic order in Tb2Sn2O7 under high pressure: From ordered spin ice to spin liquid and antiferromagnetic order Article publié en 2009 Auteurs : Isabelle Mirebeau. Goncharenko, I. Cao, H. Forget, A Réf. : PHYSICAL REVIEW B 80 (2009) 220407 We have studied the Tb2Sn2O7 ordered spin ice by neutron diffraction under an isotropic pressure of 4.6 GPa, combined with a stress of 0.3(1) GPa. Measurements down to a temperature of 0.06 K and up to 100 K probe the effect of pressure both on ground state and spin fluctuation in the paramagnetic region. In the pressure-induced ground state, the ordered spin ice structure with a k(0)=0 propagation vector persists, but it coexists with a structure with k(1)=(0,0,1). The ordered moment at 0.06 K is reduced, suggesting that pressure also enhances the spin liquid fluctuations at T similar to 0. In the paramagnetic region, applying pressure changes the short-range spin correlations and suppresses the ferromagnetic correlations. The influence of pressure is discussed considering both isotropic pressure and stress effects. Field evolution of the magnetic structures in Er2Ti2O7 through the critical point Article publié en 2010 Auteurs : Cao, HB. Isabelle Mirebeau. Gukasov, A. Bonville, P. Decorse, C Réf. : PHYSICAL REVIEW B V 82 (2010) 104431 We have measured neutron-diffraction patterns in a single-crystal sample of the pyrochlore compound Er2Ti2O7 in the antiferromagnetic phase (T=0.3 K), as a function of the magnetic field, up to 6 T, applied along the [110] direction. We determine all the characteristics of the magnetic structure throughout the critical point at H-c=2 T. As a main result, all Er moments align along the field at H-c and their values reach a minimum. Using a foursublattice self-consistent calculation, we show that the evolution of the magnetic structure and the value of the critical field are rather well reproduced using the same anisotropic exchange tensor as that accounting for the local paramagnetic susceptibility. In contrast, an isotropic exchange tensor does not yield the correct moment variations through the critical point. The model also accounts semiquantitatively for other experimental data obtained in previous works, such as the field dependence of the heat capacity, energy of the dispersionless inelastic modes and transition temperature. Field-induced magnetic structures in Tb2Ti2O7 at low temperatures: From spin-ice to spin-flip structures Article publié en 2010 Auteurs : Sazonov AP ; Gukasov A ; Isabelle Mirebeau ; Cao H ;Bonville P ; Grenier B Réf. : PHYSICAL REVIEW B 82 (2010) 174406 We studied the field-induced magnetic structures of the Tb2Ti2O7 pyrochlore by single-crystal neutron diffraction with a magnetic field applied along a [110] axis, focusing on the influence of a small misalignment. 28/02/2013 44 PUBLICATIONS PROJETS 2008 Both induced magnetic structures with k = 0 and k = (0,0,1) propagation vectors are found to be sensitive to the misalignment, which controls the magnitude and orientation of the Tb moments involved in the beta chains, with local [111] anisotropy axis perpendicular to the field. For k = 0, spin-icelike structures are observed for a misalignment of a few degrees whereas other structures, where the Tb-beta moments flip by "melting" on the field axis, occur when the field is perfectly aligned. The field evolution of the k = 0 structure is well reproduced by a molecular field model with anisotropic exchange. We give a complete symmetry analysis of the k = 0 and k = (0,0,1) magnetic structures, both being described by the basis functions of single irreducible representations. Neutron diffraction study of the chiral magnet MnGe Article publié en 2012 Auteurs : Makarova O. L.; Tsvyashchenko A. V.; Andre G.; et al. Réf. : PHYSICAL REVIEW B Volume: 85 Issue: 20 10.1103/PhysRevB.85.205205 Published: MAY 14 2012 Article Number: 205205 DOI: The magnetic structure of cubic MnGe has been determined by powder neutron diffraction. MnGe has a helical spin structure with a propagation vector k = (0,0, zeta), where zeta = 0.107(5) just below the transition temperature T-N = 170 K. The zeta value increases upon cooling and locks in to the value of 0.167(4) below 30 K. The moment value is 2.3(5)mu(B) at 2 K. The onset of the magnetic order is connected with a symmetry lowering from cubic to orthorhombic. [2008-066T] OXY SPINTRONICS Porteur : Agnès Barthélémy Thème 5 Towards Two-Dimensional Metallic Behavior at LaAlO3/SrTiO3 Interfaces Article publié en 2009 Auteurs : Copie, O. Garcia, V. Bodefeld, C. Carretero, C. Bibes, M. Herranz, G. Jacquet, E. Maurice, JL. Vinter, B. Fusil, S. Karim Bouzehouane. Jaffres, H. Barthelemy, A Réf. : PHYSICAL REVIEW LETTERS 102 (2009) 216804 Using a low-temperature conductive-tip atomic force microscope in cross-section geometry we have characterized the local transport properties of the metallic electron gas that forms at the interface between LaAlO3 and SrTiO3. At low temperature, we find that the carriers do not spread away from the interface but are confined within similar to 10 nm, just like at room temperature. Simulations taking into account both the large temperature and electric-field dependence of the permittivity of SrTiO3 predict a confinement over a few nm for sheet carrier densities larger than similar to 6x10(13) cm(-2). We discuss the experimental and simulations results in terms of a multiband carrier system. Remarkably, the Fermi wavelength estimated from Hall measurements is similar to 16 nm, indicating that the electron gas in on the verge of two dimensionality. 28/02/2013 45 PUBLICATIONS PROJETS 2008 Ferroelectric Control of Spin Polarization Article publié en 2010 Auteurs : Garcia, V. Bibes, M. Bocher, L. Valencia, S. Kronast, F. Crassous, A. Moya, X. EnouzVedrenne, S. Gloter, A. Imhoff, D. Deranlot, C. Mathur, ND. Fusil, S. Karim Bouzehouane. Barthelemy, A Réf. : SCIENCE 327 (2010) 1106-1110 A current drawback of spintronics is the large power that is usually required for magnetic writing, in contrast with nanoelectronics, which relies on "zero-current," gate-controlled operations. Efforts have been made to control the spin-relaxation rate, the Curie temperature, or the magnetic anisotropy with a gate voltage, but these effects are usually small and volatile. We used ferroelectric tunnel junctions with ferromagnetic electrodes to demonstrate local, large, and nonvolatile control of carrier spin polarization by electrically switching ferroelectric polarization. Our results represent a giant type of interfacial magnetoelectric coupling and suggest a low-power approach for spin-based information control. Giant tunnel electroresistance with PbTiO3 ferroelectric tunnel barriers Article publié en 2010 Auteurs : Crassous, A. Garcia, V. Karim Bouzehouane. Fusil, S. Vlooswijk, AHG. Rispens, G. Noheda, B. Bibes, M. Barthelemy, A Réf. : APPLIED PHYSICS LETTERS 97 (2010) 092118 The persistency of ferroelectricity in ultrathin films allows their use as tunnel barriers. Ferroelectric tunnel junctions are used to explore the tunneling electroresistance effect-a change in the electrical resistance associated with polarization reversal in the ferroelectric barrier layer-resulting from the interplay between ferroelectricity and quantum-mechanical tunneling. Here, we use piezoresponse force microscopy and conductive-tip atomic force microscopy at room temperature to demonstrate the resistive readout of the polarization state through its influence on the tunnel current in PbTiO3 ultrathin ferroelectric films. The tunnel electroresistance reaches values of 50 000% through a 3.6 nm PbTiO3 film. Interface-induced room-temperature multiferroicity in BaTiO(3) Article publié en 2011 Auteurs : Valencia, S; Crassous, A; Bocher, L; Garcia, V; Moya, X; Cherifi, RO; Deranlot, C; Bouzehouane, K; Fusil, S; Zobelli, A; Gloter, A; Mathur, ND; Gaupp, A; Abrudan, R; Radu, F; Barthelemy, A; Bibes, M Réf. : NATURE MATERIALS 10 (10): 753-758 10.1038/NMAT3098 OCT 2011 Multiferroic materials possess two or more ferroic orders but have not been exploited in devices owing to the scarcity of room-temperature examples. Those that are ferromagnetic and ferroelectric have potential applications in multi-state data storage if the ferroic orders switch independently, or in electric-field controlled spintronics if the magnetoelectric coupling is strong. Future applications could also exploit toroidal moments and optical effects that arise from the simultaneous breaking of time-reversal and space-inversion symmetries. Here, we use soft X-ray resonant magnetic scattering and piezoresponse force microscopy to reveal that, at the interface with Fe or Co, ultrathin films of the archetypal ferroelectric BaTiO(3) simultaneously possess a magnetization and a polarization that are both spontaneous and hysteretic at room temperature. Ab initio calculations of realistic interface structures provide insight into the origin of the induced moments and bring support to this new approach for creating room-temperature multiferroics. 28/02/2013 46 PUBLICATIONS PROJETS 2008 Restoration of bulk magnetic properties by strain engineering in epitaxial CoFe(2)O(4) (001) ultrathin films Article publié en 2011 Auteurs : Matzen, S.; Moussy, J. -B.; Mattana, R.; Petroff, F.; Gatel, C.; Warot-Fonrose, B.; Cezar, J. C.; Barbier, A.; Arrio, M. -A.; Sainctavit, Ph. Réf. : APPLIED PHYSICS LETTERS Volume: 99 10.1063/1.3622307 Published: AUG 1 2011 Issue: 5 Article Number: 052514 DOI: We report on the significantly enhanced in-plane magnetic properties of CoFe(2)O(4) (001) ultrathin layers (5 nm) grown on MgAl(2)O(4) (001) in comparison to films deposited on MgO (001). The predicted inverse spinel structure is confirmed by x-ray magnetic circular dichroism measurements and transmission electronic microscopy studies reveal a significant in-plane compressive strain, responsible for the strong film anisotropy. These results show that strain engineering can be used to tailor the magnetic properties of oxide ultrathin films. A large compressive strain restores bulk magnetic properties for CoFe(2)O(4) films at tunnel barrier thicknesses. (C) 2011 American Institute of Physics. [doi:10.1063/1.3622307] Ultrathin oxide films and interfaces for electronics and spintronics Article publié en 2011 Auteurs : Bibes M , Javier Villegas , Agnès Barthélémy Réf. : ADVANCES IN PHYSICS 60 (2011) Oxides have become a key ingredient for new concepts of electronic devices. To a large extent, this is due to the profusion of new physics and novel functionalities arising from ultrathin oxide films and at oxide interfaces. We present here a perspective on selected topics within this vast field and focus on two main issues. The first part of this review is dedicated to the use of ultrathin films of insulating oxides as barriers for tunnel junctions. In addition to dielectric non-magnetic epitaxial barriers, which can produce tunneling magnetoresistances in excess of a few hundred percent, we pay special attention to the possibility of exploiting the multifunctional character of some oxides in order to realize 'active' tunnel barriers. In these, the conductance across the barrier is not only controlled by the bias voltage and/or the electrodes magnetic state, but also depends on the barrier ferroic state. Some examples include spin-filtering effects using ferro- and ferrimagnetic oxides, and the possibility of realizing hysteretic, multi-state junctions using ferroelectric barriers. The second part of this review is devoted to novel states appearing at oxide interfaces. Often completely different from those of the corresponding bulk materials, they bring about novel functionalities to be exploited in spintronics and electronics architectures. We review the main mechanisms responsible for these new properties (such as magnetic coupling, charge transfer and proximity effects) and summarize some of the most paradigmatic phenomena. These include the formation of high-mobility two-dimensional electron gases at the interface between insulators, the emergence of superconductivity (or ferromagnetism) at the interface between non-superconducting (or non-ferromagnetic) materials, the observation of magnetoelectric effects at magnetic/ferroelectric interfaces or the effects of the interplay and competing interactions at all-oxide ferromagnetic/superconducting interfaces. Finally, we link up the two reviewed research fields and emphasize that the tunneling geometry is particularly suited to probe novel interface effects at oxide barrier/electrode interfaces. We close by giving some directions toward tunneling devices exploiting novel oxide interfacial phenomena. 28/02/2013 47 PUBLICATIONS PROJETS 2008 [2008-067T] CLEL Porteur : Marie-Emmanuelle Couprie Thème 6 Seed level requirement for improving the temporal coherence of a Free-Electron Laser Article publié en 2009 Auteurs : Lambert, G. Hara, T. Labat, M. Tanikawa, T. Tanaka, Y. Yabashi, M. Garzella, D. Carre, B. Marie-Emmanuelle Couprie Réf. : EPL 88 (2009) 14001 The temporal coherence of Free-Electron Laser (FEL) sources, which exhibit, in the self-amplified spontaneousemission mode, spiking spectral and temporal distributions, can be drastically improved by seeding with an external laser or high-order harmonics. Here, experiments at 160 nm put in evidence that the improvement of spectral properties (and thus temporal coherence) of the FEL radiation takes place for a larger seed intensity than the one required to overcome the shot noise. Copyright (C) EPLA, 2009 [2008-070T] LongWave Porteur : Raffaele Colombelli Thème 7 In Situ Generation of Surface Plasmon Polaritons Using a NearInfrared Laser Diode Article publié en 2012 Auteurs : Costantini, D.; Greusard, L.; Bousseksou, A.; Rungsawang, R.; Zhang, T. P.; Callard, S.; Decobert, J.; Lelarge, F.; Duan, G. -H.; De Wilde, Y.; Colombelli, R. Réf. : NANO LETTERS Volume: 12 Issue: 9 Pages: 4693-4697 DOI: 10.1021/nl302040e Published: SEP 2012 We demonstrate a semiconductor laser-based approach which enables plasmonic active devices in the telecom wavelength range. We show that optimized laser structures based on tensile-strained InGaAlAs quantum wells coupled to integrated metallic patternings enable surface plasmon generation in an electrically driven compact device. Experimental evidence of surface plasmon generation is obtained with the slit-doublet experiment in the near-field, using near-field scanning optical microscopy measurements. 28/02/2013 48 PUBLICATIONS PROJETS 2008 [2008-071T] PSYCHE Porteur : Sophie Bouchoule Axe C Addition of Si-Containing Gases for Anisotropic Etching of III-V Materials in Chlorine-Based Inductively Coupled Plasma Article publié en 2011 Auteurs : Lina Gatilova, Sophie Bouchoule, Gilles Patriarche, Stéphane Guilet Réf. : JAPANESE JOURNAL OF APPLIED PHYSICS 50 (8): Part 2 SI 10.1143/JJAP.50.08JE02 AUG 2011 We discuss the possibility of obtaining high-aspect-ratio etching of InP materials in Cl(2)- and HBr-based inductively coupled plasmas (ICP) with the addition of Si-containing gases (SiH(4) or SiCl(4)). A vertical and smooth etching profile is demonstrated in SiCl(4)/H(2) plasma. The effect of adding of a small amount of SiH(4) to a previously optimised Cl(2)/H(2) chemistry is presented, and new SiH(4)/Cl(2) and SiH(4)/HBr chemistries are proposed. Ex-situ energy-dispersive X-ray spectroscopy coupled to transmission electron microscopy (EDXTEM) is used to analyze the composition of the thin passivation layer deposited on the etched sidewalls. We show that it consists of a Si-rich silicon oxide (Si/O similar to 1) in Cl(2)/H(2)/SiH(4) chemistry, and is changed to nano-crystalline (nc-) Si in SiH(4)/Cl(2) chemistry depending on the SiH(4) percentage. Moreover, we show that deep anisotropic etching of InP independent of the electrode coverplate material can be obtained via a SiO(x) passivation mechanism with the addition of Si-containing gases. (C) 2011 The Japan Society of Applied Physics High-aspect-ratio inductively coupled plasma etching of InP using SiH4/Cl-2: Avoiding the effect of electrode coverplate material Article publié en 2011 Auteurs : Gatilova, L; Bouchoule, S; Guilet, S; Patriarche, G Réf. : JOURNAL OF VACUUM SCIENCE & TECHNOLOGY B 29 (2)(2011) 020601 A new SiH4/Cl-2 chemistry is proposed for the high-aspect-ratio etching of InP-based heterostructures. Anisotropic etching is obtained through the deposition of a SiOx passivation layer on the etched sidewalls. SiH4 has been chosen as a single precursor for both Si and H species that are necessary to promote the passivation process. Previously developed Cl-2/H-2- or HBr-based chemistries for anisotropic etching of laser waveguides or vertical microcavities require a silicon wafer below the InP samples in order to assist the passivation mechanism. In contrast, the authors show that a SiOx passivation can be achieved and maintained almost independent of the nature of the wafer surface when SiH4 is added. This is of practical importance for the processing of III-V wafers having the same size as the electrode or for III-V heterogeneous integration when IIIV dies bonded onto a 200/300 mm diameter wafer have to be etched. Smooth, notch-free, anisotropic etching of InGa(Al)As/InP heterostructures is demonstrated. Ex situ energy-dispersive x-ray spectroscopy coupled to a transmission electron microscope is used to analyze the composition of the thin passivation layer deposited on the sidewalls of etched features. The authors show that the passivation layer consists of a Si-rich silicon oxide (Si/O similar to 1) in Cl-2/H-2/SiH4 chemistry and is changed to nanocrystalline Si in SiH4/Cl-2 chemistry depending on the SiH4 concentration in the feed gas. An aspect ratio as high as 28 is obtained in the latter case. (C) 2011 American Vacuum Society. 28/02/2013 49 PUBLICATIONS PROJETS 2008 [2008-072T] POMS Porteur : Patrick Davidson Thème 3 A PGSE-NMR Study of Molecular Self-Diffusion in Lamellar Phases Doped with Polyoxometalates Article publié en 2010 Auteurs : Poulos, AS. Constantin, D. Davidson, P. Imperor, M. Judeinstein, P. Pansu, B Réf. : JOURNAL OF PHYSICAL CHEMISTRY B 114 (2010) 220-227 Using pulsed gradient spin-echo NMR, We studied molecular self-diffusion in aligned samples of a hybrid lyotropic lamellar L-alpha, phase. This composite organic-inorganic material was obtained by doping the lamellar phase of the nonionic surfactant Brij-30 With the [PW12O40](3-) polyoxometalate (PO M). Both water and POM self-diffusion display a large anisotropy, as diffusion is severely restricted along the normal to the bilayers. Water diffusion in planes parallel to the bilayers does not depend oil the POM concentration but depends on the lamellar period, which is due to a variable Fraction of "bound" water molecules. POM diffusion in the hybrid L-alpha phase is almost 2 orders of magnitude slower than in aqueous Solution. Moreover, it is not at all affected by the thickness of the aqueous medium separating the bilayers. This proves that the POM nanoparticles do not freely diffuse in the interbilayer aqueous space but adsorb onto the PEG brushes that cover both sides of the surfactant bilayers. Communications: Short-range dynamics of a nematic liquidcrystalline phase Article publié en 2010 Auteurs : Poulos, AS. Constantin, D. Davidson, P. Pansu, B. Freyssingeas, E. Madsen, A. Chaneac, C Réf. : JOURNAL OF CHEMICAL PHYSICS 132 (2010) 091101 Using x-ray photon correlation spectroscopy, we studied the dynamics in the nematic phase of a nanorod suspension. The collective diffusion coefficient in the plane perpendicular to the director varies sharply with the wave vector. Combining the structure factor and the diffusion coefficient, we find that the hydrodynamic function of the phase decreases by more than a factor of 10 when going from length scales comparable to the interparticle distance toward larger values. Thus, the collective dynamics of the nematic phase experiences strong and scale-dependent slowing down, in contrast with isotropic suspensions of slender rods or of spherical particles. Orientational Order of Colloidal Disk-Shaped Particles under ShearFlow Conditions: a Rheological-Small-Angle X-ray Scattering Study Article publié en 2010 Auteurs : Bihannic, I; Baravian, C; Duval, JFL; Paineau, E; Meneau, F; Levitz, P; de Silva, JP; Davidson, P; Michot, LJ Réf. : JOURNAL OF PHYSICAL CHEMISTRY B 114 (2010) The structure of a colloidal dispersion consisting of anisometric natural clay particles (beidellite) was followed under shear-flow conditions by small-angle X-ray scattering (SAXS) measurements in a Couette-type cell. It is 28/02/2013 50 PUBLICATIONS PROJETS 2008 shown that in this shear-thinning dispersion an orientational order develops with increasing shear rate. By use of two different geometrical configurations for SAXS measurements, corresponding to incident beam parallel and perpendicular to flow velocity gradient (radial and tangential configurations, respectively), it is observed that SAXS patterns are anisotropic in both geometries, meaning that particles tend to align along a preferred orientation with their normal in velocity gradient direction, and further they partly rotate around flow streamlines. Quantitative interpretation of these results is successfully achieved upon derivation of a probability distribution function accounting for biaxial particle orientation. From this distribution and following geometrical arguments, the viscosity of the suspension was calculated for each shear rate and found to correctly compare with rheological measurements, thereby appropriately relating the anisotropy of the SAXS patterns to macroscopic flow behavior of the suspension. [2008-075T] Magnetic-Graphene Porteur : Marc Goerbig Thème 4 Spin-flip excitations, spin waves, and magnetoexcitons in graphene Landau levels at integer filling factors Article publié en 2010 Auteurs : Roldan R ; Julien FuchsN ; Marc GoerbigO Réf. : PHYSICAL REVIEW B 82 (2010) 205418 We study collective electronic excitations in graphene in the integer quantum-Hall regime, concentrating mainly on excitations with spin reversal such as spin-flip and spin-wave excitations. We show that these excitations are correctly accounted for in the time-dependent Hartree-Fock and strong magnetic field approximations, in contrast to spin-conserving (magnetoexciton) modes which involve a strong Landau-level mixing at nonzero wave vectors. The collective excitations are discussed in view of prominent theorems, such as Kohn's and Larmor's. Whereas the latter remains valid in graphene and yields insight into the understanding of spindependent modes, Kohn's theorem does not apply to relativistic electrons in graphene. We finally calculate the exchange correction to the chemical potential in the weak magnetic field limit. The magnetic field particle-hole excitation spectrum in doped graphene and in a standard two-dimensional electron gas Article publié en 2010 Auteurs : Roldan, R. Marc Goerbig, O. Julien FuchsN Réf. : SEMICONDUCTOR SCIENCE AND TECHNOLOGY 25 (2010) 034005 The particle-hole excitation spectrum for doped graphene is calculated from the dynamical polarizability. We study the zero and finite magnetic field cases and compare them to the standard two-dimensional electron gas. The effects of electron-electron interaction are included within the random-phase approximation. From the obtained polarizability, we study the screening effects and the collective excitations (plasmon, magneto-excitons, upper-hybrid mode and linear magneto-plasmons). We stress the differences with the usual 2DEG. 28/02/2013 51 PUBLICATIONS PROJETS 2008 Theory of Bernstein modes in graphene Article publié en 2011 Auteurs : Roldan, R; Marc GoerbigO; Julien FuchsN Réf. : PHYSICAL REVIEW B 83 (20): Art. No. 205406 MAY 17 2011 We present a theoretical description of Bernstein modes that arise as a result of the coupling between plasmonlike collective excitations (upper-hybrid mode) and inter-Landau-level excitations, in graphene in a perpendicular magnetic field. These modes, which are apparent as avoided level crossings in the spectral function obtained in the random-phase approximation, are described to great accuracy in a phenomenological model. Bernstein modes, which may be measured in inelastic light-scattering experiments or in photoconductivity spectroscopy, are a manifestation of the Coulomb interaction between the electrons and may be used for a high-precision measurement of the upper-hybrid mode at small nonzero wave vectors. [2008-080T] GEOFLOW Porteur : Frédéric Moisy Thème 3 Viscous spreading of an inertial wave beam in a rotating fluid Article publié en 2010 Auteurs : Cortet, PP. Lamriben, C. Frédéric Moisy Réf. : PHYSICS OF FLUIDS 22 (2010) 086603 We report experimental measurements of inertial waves generated by an oscillating cylinder in a rotating fluid. The two-dimensional wave takes place in a stationary cross-shaped wavepacket. Velocity and vorticity fields in a vertical plane normal to the wavemaker are measured by a corotating particle image velocimetry system. The viscous spreading of the wave beam and the associated decay of the velocity and vorticity envelopes are characterized. They are found in good agreement with the similarity solution of a linear viscous theory, derived under a quasiparallel assumption similar to the classical analysis of Thomas and Stevenson ["A similarity solution for viscous internal waves," J. Fluid Mech. 54, 495 (1972)] for internal waves. (C) 2010 American Institute of Physics. [doi:10.1063/1.3483468] Direct Measurements of Anisotropic Energy Transfers in a Rotating Turbulence Experiment Article publié en 2011 Auteurs : Lamriben C, Cortet PP,Frédéric Moisy Réf. : PHYSICAL REVIEW LETTERS 107 (2): 10.1103/PhysRevLett.107.024503 We investigate experimentally the influence of a background rotation on the energy transfers in decaying grid turbulence. The anisotropic energy flux density F(r) = <delta u(delta u)(2)>, where delta u is the vector velocity increment over separation r, is determined for the first time by using particle image velocimetry. We show that rotation induces an anisotropy of the energy flux del.F, which leads to an anisotropy growth of the energy distribution E(r) = <(delta u)(2)>, in agreement with the von Karman-Howarth-Monin equation. Surprisingly, 28/02/2013 52 PUBLICATIONS PROJETS 2008 our results prove that this anisotropy growth is essentially driven by a nearly radial, but orientation-dependent, energy flux density F(r). Excitation of inertial modes in a closed grid turbulence experiment under rotation Article publié en 2011 Auteurs : Lamriben, C; Cortet, PP; Frédéric Moisy; Maas, LRM Réf. : PHYSICS OF FLUIDS 23 (2011) 015102 We report an experimental study of the decay of grid-generated turbulence in a confined geometry submitted to a global rotation. Turbulence is generated by rapidly towing a grid in a parallelepipedic water tank. The velocity fields of a large number of independent decays are measured in a vertical plane parallel to the rotation axis using a corotating particle image velocimetry system. We first show that, when a "simple" grid is used, a significant amount of the kinetic energy (typically 50%) is stored in a reproducible flow composed of resonant inertial modes. The spatial structure of those inertial modes, extracted by band-pass filtering, is found compatible with the numerical results of L. R. M. Maas [Fluid Dyn. Res. 33, 373 (2003)]. The possible coupling between these modes and turbulence suggests that turbulence cannot be considered as freely decaying in this configuration. We demonstrate however that these inertial modes may be significantly reduced (down to 15% of the total energy) by adding a set of inner tanks attached to the grid. These results suggest that it is possible to produce an effectively freely decaying rotating turbulence in a confined geometry. (c) 2011 American Institute of Physics. CHEMO-hydrodynamic coupling between forced advection in porous media and self-sustained chemical waves Article publié en 2012 Auteurs : Atis, S.; Saha, S.; Auradou, H.; Martin, J.; Rakotomalala, N.; Talon, L.; Salin, D. Réf. : CHAOS Volume: 22 Issue: 3 SEP 2012 Article Number: 037108 DOI: 10.1063/1.4734489 Published: Autocatalytic reaction fronts between two reacting species in the absence of fluid flow, propagate as solitary waves. The coupling between autocatalytic reaction front and forced simple hydrodynamic flows leads to stationary fronts whose velocity and shape depend on the underlying flow field. We address the issue of the chemico-hydrodynamic coupling between forced advection in porous media and self-sustained chemical waves. Towards that purpose, we perform experiments over a wide range of flow velocities with the well characterized iodate arsenious acid and chlorite-tetrathionate autocatalytic reactions in transparent packed beads porous media. The characteristics of these porous media such as their porosity, tortuosity, and hydrodynamics dispersion are determined. In a pack of beads, the characteristic pore size and the velocity field correlation length are of the order of the bead size. In order to address these two length scales separately, we perform lattice Boltzmann numerical simulations in a stochastic porous medium, which takes into account the log-normal permeability distribution and the spatial correlation of the permeability field. In both experiments and numerical simulations, we observe stationary fronts propagating at a constant velocity with an almost constant front width. Experiments without flow in packed bead porous media with different bead sizes show that the front propagation depends on the tortuous nature of diffusion in the pore space. We observe microscopic effects when the pores are of the size of the chemical front width. We address both supportive co-current and adverse flows with respect to the direction of propagation of the chemical reaction. For supportive flows, experiments and simulations allow observation of two flow regimes. For adverse flow, we observe upstream and downstream front motion as well as static front behaviors over a wide range of flow rates. In order to understand better these observed static state fronts, flow experiments around a single obstacle were used to delineate the range of steady state behavior. A model using the "eikonal thin front limit" explains the observed steady states. (C) 2012 American Institute of Physics. [http://dx.doi.org/10.1063/1.4734489] 28/02/2013 53 PUBLICATIONS PROJETS 2008 Earth rotation prevents exact solid-body rotation of fluids in the laboratory Article publié en 2012 Auteurs : Boisson, J.; Cebron, D.; Moisy, F.; Cortet, P. -P. Réf. : EPL Volume: 98 Published: JUN 2012 Issue: 5 Article Number: 59002 DOI: 10.1209/0295-5075/98/59002 We report direct evidence of a secondary flow excited by the Earth rotation in a water-filled spherical container spinning at constant rotation rate. This so-called tilt-over flow essentially consists in a rotation around an axis which is slightly tilted with respect to the rotation axis of the sphere. In the astrophysical context, it corresponds to the flow in the liquid cores of planets forced by precession of the planet rotation axis, and it has been proposed to contribute to the generation of planetary magnetic fields. We detect this weak secondary flow using a particle image velocimetry system mounted in the rotating frame. This secondary flow consists in a weak rotation, thousand times smaller than the sphere rotation, around a horizontal axis which is stationary in the laboratory frame. Its amplitude and orientation are in quantitative agreement with the theory of the tilt-over flow excited by precession. These results show that setting a fluid in a perfect solid-body rotation in a laboratory experiment is impossible -unless by tilting the rotation axis of the experiment parallel to the Earth rotation axis. Copyright (C) EPLA, 2012 Inertial waves and modes excited by the libration of a rotating cube Article publié en 2012 Auteurs : Boisson, Jean; Lamriben, Cyril; Maas, Leo R. M.; Cortet, Pierre-Philippe; Moisy, Frederic Réf. : PHYSICS OF FLUIDS Volume: 24 Issue: 7 Published: JUL 2012 Article Number: 076602 DOI: 10.1063/1.4731802 We report experimental measurements of the flow in a cubic container submitted to a longitudinal libration, i.e., a rotation modulated in time. Velocity fields in a vertical and a horizontal plane are measured in the librating frame using a corotating particle image velocimetry system. When the libration frequency sigma(0) is smaller than twice the mean rotation rate, Omega(0), inertial waves can propagate in the interior of the fluid. At arbitrary excitation frequencies sigma(0) < 2 Omega(0), the oscillating flow shows two contributions: (i) a basic flow induced by the libration motion, and (ii) inertial wave beams propagating obliquely upward and downward from the horizontal edges of the cube. In addition to these two contributions, inertial modes may also be excited at some specific resonant frequencies. We characterize in particular the resonance of the mode of lowest order compatible with the symmetries of the forcing, noted [2,1,+]. By comparing the measured flow fields to the expected inviscid inertial modes computed numerically [L. R. M. Maas, "On the amphidromic structure of inertial waves in rectangular parallelepiped," Fluid Dyn. Res. 33, 373 (2003)], we show that only a subset of inertial modes, matching the symmetries of the forcing, can be excited by the libration. (C) 2012 American Institute of Physics. [http://dx.doi.org/10.1063/1.4731802] Relation between first arrival time and permeability in self-affine fractures with areas in contact Article publié en 2012 Auteurs : Talon L.; Auradou H.; Hansen A. Réf. : EPL Volume: 97 Published: MAR 2012 28/02/2013 Issue: 6 Article Number: 68009 DOI: 10.1209/0295-5075/97/68009 54 PUBLICATIONS PROJETS 2008 We demonstrate that the first arrival times in dispersive processes in self-affine fractures are governed by the same length scale characterizing the fractures as that which controls their permeability. In one-dimensional channel flow this length scale is the aperture of the bottle neck, i.e., the region having the smallest aperture. In two dimensions, the concept of a bottle neck is generalized to that of a minimal path normal to the flow. The length scale is then the average aperture along this path. There is a linear relationship between the first arrival time and this length scale, even when there is strong overlap between the fracture surfaces creating areas with zero permeability. We express the first arrival time directly in terms of the permeability. Copyright (C) EPLA, 2012 Stokes flow paths separation and recirculation cells in X-junctions of varying angle Article publié en 2012 Auteurs : Cachile M.; Talon L.; Gomba J. M.; et al. Réf. : PHYSICS OF FLUIDS Volume: 24 Issue: 2 Article Number: 021704 DOI: 10.1063/1.3690100 Published: FEB 2012 Fluid and solute transfer in X-junctions between straight channels is shown to depend critically on the junction angle alpha in the Stokes flow regime. Experimentally, water and a water-dye solution are injected at equal flow rates in two facing channels of the junction. Planar laser induced fluorescence (PLIF) measurements show that the largest part of each injected fluid "bounces back" preferentially into the outlet channel at the lowest angle to the injection; this is opposite to the inertial case and requires a high curvature of the corresponding streamlines. The proportion of this fluid in the other channel decreases from 50% at alpha = 90 degrees to 0% at a threshold angle. These counterintuitive features reflect the minimization of energy dissipation for Stokes flows. Finite elements numerical simulations of a 2D Stokes flow of equivalent geometry confirm these results and show that, below the threshold angle alpha(c) = 33.8 degrees, recirculation cells are present in the center part of the junction and separate the two injected flows of the two solutions. Reducing further alpha leads to the appearance of new recirculation cells with lower flow velocities. (c) 2012 American Institute of Physics. [http://dx.doi.org.gate4.inist.fr/10.1063/1.3690100] [2008-082T] NonFermiSupra Porteur : Marcelo Rozenberg Thème 4 Hund's coupling and its key role in tuning multiorbital correlations Article publié en 2011 Auteurs : de' Medici, L Réf. : PHYSICAL REVIEW B 83 (20): Art. No. 205112 MAY 17 2011 PRL (2011) 107, 256 401 It is shown how, in multiband materials, the Hund's coupling plays a crucial role in tuning the degree of electronic correlation. While in half-filled systems it enhances the correlations, in all other cases it pushes the boundary for the Mott transition at very high critical couplings. Moreover in weakly hybridized nondegenerate systems the Hund's coupling plays the role of band decoupler, causing a change from a collective to an individual band behavior, due to the freezing of orbital fluctuations. In this situation the physics is strongly dependent on individual filling and electronic structure of each band, and orbital-selective Mott transitions (or 28/02/2013 55 PUBLICATIONS PROJETS 2008 even a cascade of such transitions) are to be expected. More generally a heavy differentiation in the actual degree of correlation of different bands arises and the system can show both weakly and strongly correlated electrons. Janus-Faced Influence of Hund's Rule Coupling in Strongly Correlated Materials Article publié en 2011 Auteurs : de' Medici Luca; Mravlje Jernej; Georges Antoine Réf. : PHYSICAL REVIEW LETTERS Volume: 107 Issue: 25 10.1103/PhysRevLett.107.256401 Published: DEC 12 2011 Article Number: 256401 DOI: We show that in multiband metals the correlations are strongly affected by Hund's rule coupling, which depending on the filling promotes metallic, insulating or bad-metallic behavior. The quasiparticle coherence and the proximity to a Mott insulator are influenced distinctly and, away from single- and half-filling, in opposite ways. A strongly correlated bad metal far from a Mott phase is found there. We propose a concise classification of 3d and 4d transition-metal oxides within which the ubiquitous occurrence of strong correlations in Ru- and Cr-based oxides, as well as the recently measured high Neel temperatures in Tc-based perovskites are naturally explained. Role of oxygen-oxygen hopping in the three-band copper-oxide model: Quasiparticle weight, metal insulator and magnetic phase boundaries, gap values, and optical conductivity Article publié en 2011 Auteurs : Wang, X; de' Medici, L; Millis, AJ Réf. : PHYSICAL REVIEW B 83 (2011) 094501 We investigate the effect of oxygen-oxygen hopping on the three-band copper-oxide model relevant to high-T-c cuprates, finding that the physics is changed only slightly as the oxygen-oxygen hopping is varied. The location of the metal-insulator phase boundary in the plane of interaction strength and charge-transfer energy shifts by similar to 0.5 eV or less along the charge-transfer axis, the quasiparticle weight has approximately the same magnitude and doping dependence, and the qualitative characteristics of the electron-doped and hole-doped sides of the phase diagram do not change. The results confirm the identification of La2CuO4 as a material with an intermediate correlation strength. However, the magnetic phase boundary as well as higher energy features of the optical spectrum are found to depend on the magnitude of the oxygen-oxygen hopping. We compare our results to previously published one-band and three-band model calculations. Covalency, double-counting, and the metal-insulator phase diagram in transition metal oxides Article publié en 2012 Auteurs : Wang, Xin; Han, M. J.; de' Medici, Luca; Park, Hyowon; Marianetti, C. A.; Millis, Andrew J. Réf. : PHYSICAL REVIEW B Volume: 86 Issue: 19 10.1103/PhysRevB.86.195136 Published: NOV 26 2012 Article Number: 195136 DOI: Dynamical mean field theory calculations are used to show that for late transition metal oxides a critical variable for the Mott/charge-transfer transition is the number of d electrons, which is determined by charge transfer from oxygen ions. Insulating behavior is found only for a narrow range of d occupancy, irrespective of the size of the intra-d Coulomb repulsion. The result is useful in interpreting "density functional + U" and "density functional plus dynamical mean field" methods in which additional correlations are applied to a specific set of orbitals and 28/02/2013 56 PUBLICATIONS PROJETS 2008 an important role is played by the "double counting correction" which dictates the occupancy of these correlated orbitals. General considerations are presented and are illustrated by calculations for two representative transition metal oxide systems: layered perovskite Cu-based high-T-c materials, an orbitally nondegenerate electronically quasi-two-dimensional system, and pseudocubic rare earch nickelates, an orbitally degenerate electronically three-dimensional system. Density functional calculations yield d occupancies very far from the Mott metalinsulator phase boundary in the nickelate materials, but closer to it in the cuprates, indicating the sensitivity of theoretical models of the cuprates to the choice of double counting correction, and corroborating the critical role of lattice distortions in attaining the experimentally observed insulating phase in the nickelates. Path to poor coherence in the periodic Anderson model from Mott physics and hybridization Article publié en 2012 Auteurs : Amaricci A.; Medici L. De'; Sordi G.; et al. Réf. : PHYSICAL REVIEW B Volume: 85 Issue: 23 10.1103/PhysRevB.85.235110 Published: JUN 5 2012 Article Number: 235110 DOI: We investigate the anomalous metal arising from hole-doping the Mott insulating state in the periodic Anderson model. Using dynamical mean-field theory we show that, as opposed to the electron-doped case, in the holedoped regime the hybridization between localized and delocalized orbitals leads to the formation of composite quasiparticles reminiscent of the Zhang-Rice singlets. We compute the coherence temperature of this state, showing its extremely small value at low doping. As a consequence the weakly doped Mott state deviates from the predictions of Fermi-liquid theory already at small temperatures. The onset of the Zhang-Rice state and of the consequent poor coherence is due to the electronic structure in which both localized and itinerant carriers have to be involved in the formation of the conduction states and to the proximity to the Mott state. By investigating the magnetic properties of this state, we discuss the relation between the anomalous metallic properties and the behavior of the magnetic degrees of freedom. [2008-086T] XDIF Porteur : Hamed Merdji Thème 6 Single-shot Femtosecond X-Ray Holography Using Extended References Article publié en 2010 Auteurs : Gauthier D, Guizar-Sicairos M, Ge X, Boutu W , Carre B, Fienup JR, Hamed Merdji Réf. : PHYSICAL REVIEW LETTERS 105 (2010) 093901 In the context of x-ray lensless imaging, we present a recent approach for Fourier transform holography based on the use of extended references. Major advances shown here rely on a high signal efficiency and on the direct image reconstruction of the object performed by a simple linear derivative. Moreover, the extended holographic reference is easy to manufacture and can be applied to a variety of imaging experiments. Here we demonstrate single-shot imaging with a table-top, laser-based coherent soft x-ray source. A spatial resolution of 110 nm was obtained with an integration time of 20 fs. 28/02/2013 57 PUBLICATIONS PROJETS 2008 [2008-088T] OPODRAG Porteur : Fabien Bretenaker Thème 7 Stimulated Raman scattering in an optical parametric oscillator based on periodically poled MgO-doped stoichiometric LiTaO3 Article publié en 2009 Auteurs : My TH, Robin O, Mhibik, O, Fabien Bretenhacker, C. Drag Réf. : OPTICS EXPRESS 17 (2009) 5912-5918 The evolution of the spectrum of a singly resonant optical parametric oscillator based on an MgO-doped periodically poled stoichiometric lithium tantalate crystal is observed when the pump power is varied. The onset of cascade Raman lasing due to stimulated Raman scattering in the nonlinear crystal is analyzed. Spurious frequency doubling and sum-frequency generation phenomena are observed and understood. A strong reduction of the intracavity Raman scattering is obtained by a careful adjustment of the cavity losses. (C) 2009 Optical Society of America Frequency stabilization at the kilohertz level of a continuous intracavity frequency-doubled singly resonant optical parametric oscillator Article publié en 2010 Auteurs : Mhibik, O. My, TH. Paboeuf, D. Fabien Bretenaker. Drag, C Réf. : OPTICS LETTERS 35 (2010) 2364-2366 A continuous intracavity frequency-doubled singly resonant optical parametric oscillator (OPO) is stabilized to the side of the transmission peak of a medium finesse Fabry-Perot cavity. The narrow bandwidth of the frequency noise of this OPO allows this simple scheme to lead to a stability of a few kilohertz with respect to the locking etalon. The system, operating in the visible domain, remains locked for more than 1 h. (C) 2010 Optical Society of America Diode-pumped Pr:BaY(2)F(8) continuous-wave orange laser Article publié en 2011 Auteurs : D Paboeuf, O Mhibik, F Bretenaker,P Goldner, D Parisi, M Tonelli Réf. : OPTICS LETTERS Published: JAN 15 2011 Volume: 36 Issue: 2 Pages: 280-282 DOI: 10.1364/OL.36.000280 We report the realization of the continuous wave laser emission in the orange at 607 nm from a Pr: BaY(2)F(8) (Pr:BYF) crystal pumped by a blue GaN laser diode. A maximal output power of 78 mW is obtained in a quasisingle transverse mode beam. The effect of reabsorption losses at the laser wavelength is also evidenced. (C) 2011 Optical Society of America. 28/02/2013 58 PUBLICATIONS PROJETS 2008 Sub-kHz-level relative stabilization of an intracavity doubled continuous wave optical parametric oscillator using Pound-DreverHall scheme Article publié en 2011 Auteurs : O Mhibik, D Paboeuf, C Drag, F Bretenaker Réf. : OPTICS EXPRESS 19 (19): 18049-18057 SEP 12 2011 We report the relative frequency stabilization of an intracavity frequency doubled singly resonant optical parametric oscillator on a Fabry-Perot etalon. The red/orange radiation produced by the frequency doubling of the intracavity resonant idler is stabilized using the Pound-Drever-Hall locking technique. The relative frequency noise of this orange light, when integrated from 1 Hz to 50 kHz, corresponds to a standard deviation of 700 Hz. The frequency noise of the pump laser is shown experimentally to be transferred to the non resonant signal beam. Optimization of the resonant wave output coupling of a singly resonant optical parametric oscillator using an intracavity plate Article publié en 2012 Auteurs : Paboeuf, D.; Mhibik, O.; Bretenaker, F.; Drag, C. Réf. : APPLIED PHYSICS B-LASERS AND OPTICS Volume: 108 10.1007/s00340-012-4946-4 Published: AUG 2012 Issue: 2 Pages: 289-293 DOI: We present a technique allowing us to optimize the output coupling of the resonant wave of a singly resonant optical parametric oscillator (SRO). By inserting a silica plate inside the cavity and tilting it around the Brewster angle, the output coupling of the SRO can be easily varied. This technique combines in principle the advantage of an efficient output coupling together with the possibility of controlling the frequency of the resonant wave of the SRO. We use this plate inside a 532-nm-pumped SRO to extract 1.6 W at 1.2 mu m with a pump depletion of 80 %. We also show the possibility of determining the intracavity loss of the OPO, which is a useful parameter regarding its optimization. Ultranarrow resonance due to coherent population oscillations in a Lambda-type atomic system Article publié en 2012 Auteurs : Laupretre T.; Kumar S.; Berger P.; et al. Réf. : PHYSICAL REVIEW A Volume: 85 Issue: 5 10.1103/PhysRevA.85.051805 Published: MAY 24 2012 Article Number: 051805 DOI: It is well known that ultranarrow electromagnetically induced transparency (EIT) resonances can be observed in atomic gases at room temperature. We report here the experimental observation of another type of ultranarrow resonance, as narrow as the EIT ones, in a Lambda system selected by light polarization in metastable He-4 at room temperature. It is shown to be due to coherent population oscillations in an open two-level system (TLS). For perpendicular linearly polarized coupling and probe beams, this system can be considered as two coupled open TLSs, in which the ground-state populations exhibit antiphase oscillations. We also predict theoretically that in the case of two parallel polarizations, the system would behave like a closed TLS, and the narrow resonance associated with these oscillations would disappear. 28/02/2013 59 PUBLICATIONS PROJETS 2008 [2008-091T] CAAS Porteur : P. Voisin Axe B Anisotropic magneto-resistance in a GaMnAs-based single impurity tunnel diode: A tight binding approach Article publié en 2012 Auteurs : Nestoklon, MO; Krebs, O; Jaffres, H; Ruttala, S; George, JM; Jancu, JM; Voisin, P Réf. : APPLIED PHYSICS LETTERS, 100 (6):10.1063/1.3683525 FEB 6 2012 Using an advanced tight-binding approach, we estimate the anisotropy of the tunnel transmission associated with the rotation of the 5/2 spin of a single Mn atom forming an acceptor state in GaAs and located near an AlGaAs tunnel barrier. Significant anisotropies in both in-plane and out-of-plane geometries are found, resulting from the combination of the large spin-orbit coupling associated with the p-d exchange interaction, cubic anisotropy of heavy-hole dispersion and the low C-2v symmetry of the chemical bonds. (C) 2012 American Institute of Physics. [doi: 10.1063/1.3683525] Spin splitting of electron states in (110) quantum wells: Symmetry analysis and k.p theory versus microscopic calculations Article publié en 2012 Auteurs : Nestoklon M. O.; Tarasenko S. A.; Jancu J. -M.; et al. Réf. : PHYSICAL REVIEW B Volume: 85 Issue: 20 10.1103/PhysRevB.85.205307 Published: MAY 9 2012 Article Number: 205307 DOI: Spin splittings in quantum wells have attracted considerable attention over the past decade due to potential application of semiconductor spin properties to "spintronic devices." Recent experimental results stimulate theoretical investigations of new physical situations like unconventional growth directions. Here we focus on electron spin properties in (110)-oriented quantum wells that are of particular interest because qualitative symmetry analysis shows that spin relaxation by the D'yakonov-Perel' mechanism should be strongly suppressed in this geometry. We combine symmetry analysis, envelope function theory, and tight-binding calculation and obtain quantitative description of the in-plane wave vector, well width, and applied electric field dependence of the spin structure of electron subbands in (110) quantum wells. 28/02/2013 60 PUBLICATIONS PROJETS 2008 [2008-091T] CAAS 1 & [2012-019T] CAAS 2 Porteur : P. Voisin Axe B Anomalous suppression of valley splittings in lead salt nanocrystals without inversion center Article publié en 2012 Auteurs : Poddubny, A. N.; Nestoklon, M. O.; Goupalov, S. V. Réf. : PHYSICAL REVIEW B Volume: 86 Issue: 3 10.1103/PhysRevB.86.035324 Published: JUL 25 2012 Article Number: 035324 DOI: We demonstrate that confinement-induced intervalley splittings of electron energy levels in PbSe and PbS nanocrystals are sensitive to the arrangement of atoms within a nanocrystal. The splittings are strongly suppressed for stoichiometric nanocrystals of T-d point symmetry lacking a center of inversion as opposed to nonstoichiometric nanocrystals of O-h point symmetry having an inversion center. Our findings are supported by both atomistic sp(3)d(5)s* tight-binding calculations and a symmetry analysis. [2008-092T] ALVAREZ Porteur : Tiberiu Minea Axe C Nanostructured tantalum nitride films as buffer-layer for carbon nanotube growth Article publié en 2011 Auteurs : Jin C, Delmas M, Aubert P, Alvarez F, Minea T, Hugon MC, Bouchet-Fabre, B Réf. : THIN SOLID FILMS 519 (12): 4097-4100 Sp. Iss. SI APR 1 Tantalum nitride (TaNx) films are usually used as barriers to the diffusion of copper in the substrate for electronic devices. In the present work, the TaNx coating plays an extra role in the iron catalyzed chemical vapor deposition production of carbon nanotubes (CNT). The CNTs were grown at 850 degrees C on TaNx films prepared by radio frequency magnetron sputtering. The correlation between the CNT morphology and growth rate, and the pristine TaNx film nature, is investigated by comparing the evolution of the nano-composition, roughness and nano-crystallinity of the TaNx films both after annealing and CVD at 850 degrees C. 2011 Published by Elsevier B.V. 28/02/2013 61 PUBLICATIONS PROJETS 2008 [2008-095T] STP Porteur : Nita Dragoe Axe C Electrical transport properties of Mn-doped LaFeAsO oxypnictide Article publié en 2009 Auteurs : Berardan, D. Loreynne Loreynne Pinsard-Gaudart. Nita Dragoe Réf. : JOURNAL OF ALLOYS AND COMPOUNDS 481 (2009) 470-472 We report on the electrical transport properties of the Mn-doped LaFe1-xMnxAsO oxypnictide system. We show that the substitution of iron by manganese in the FeAs layer leads to a gradual expansion of the lattice parameters and of the Fe-As and Fe-Fe bond lengths, as well as a change in the angles of the FeAs4 tetrahedron which becomes more regular. The structural transition from tetragonal to orthorhombic coupled to the emergence of a spin density wave is rapidly suppressed by Mn doping. Interestingly, Mn doping does not lead to p-type behaviour. Moreover, no superconducting transition is observed, and the system evidences a metalsemiconductor transition around x = 0.03. Thus, there is apparently no symmetric behaviour of the manganese doping and cobalt doping in the FeAs layer of the LaFeAsO system. (C) 2009 Elsevier B.V. All rights reserved. Bi1-xSrxCuSeO oxyselenides as promising thermoelectric materials Article publié en 2010 Auteurs : Zhao, LD. Berardan, D. Pei, YL. Byl, C. Loreynne Loreynne Pinsard-Gaudart. Nita Dragoe Réf. : APPLIED PHYSICS LETTERS 97 (2010) 092118 p-type BiCuSeO, a layered oxyselenide composed of conductive (Cu2Se2)(2-) layers alternately stacked with insulating (Bi2O2)(2+) layers, shows an enhancement of the electrical conductivity after substituting Bi3+ by Sr2+, from 470 S m(-1) (BiCuSeO) to 4.8 x 10(4) S m(-1) (Bi0.85Sr0.15CuSeO) at 293 K. Coupled to high Seebeck coefficients, this leads to promising values of the thermoelectric power factor that exceeds 500 mu W m(-1) K-2 at 873 K. Moreover, the thermal conductivity of these layered compounds is lower than 1 W m(-1) K1 at 873 K. Maximum ZT values reach 0.76 at 873 K, making this family promising for thermoelectric applications in the medium temperature range. (C) 2010 American Institute of Physics. [doi:10.1063/1.3485050] Effects of Co doping on the transport properties and superconductivity in CeFe1-xCoxAsO Article publié en 2010 Auteurs : Zhao, LD. Berardan, D. Byl, C. Loreynne Loreynne Pinsard-Gaudart. Nita Dragoe Réf. : JOURNAL OF PHYSICS-CONDENSED MATTER 22 (2010) 115701 A series of CeFe1-xCoxAsO oxyarsenide compounds with Co doping on iron sites (x = 0-0.2) have been synthesized by a solid state reaction method. The effects of Co doping on the electrical transport properties and superconductivity were analyzed with a special emphasis on the analysis of thermopower. Undoped CeFeAsO shows an electrical resistivity anomaly at about 150 K, which was ascribed to a spin-density-wave (SDW) instability. This anomaly is suppressed and a superconducting transition occurs at T-c = 3.2 K in CeFe0.95Co0.05AsO, the maximum superconducting transition temperature (T-c) of 12.5 K is observed in CeFe0.90Co0.10AsO, and the thermopower is increased by the Co doping. As has been previously suggested, 28/02/2013 62 PUBLICATIONS PROJETS 2008 the emergence of superconductivity seems to be closely linked to the thermopower, and there is a close correlation between Tc and the thermopower, both showing a similar dome-like doping dependence. Electrical transport properties of F-doped LaFeAsO oxypnictide Article publié en 2010 Auteurs : Zhao LD ; Berardan D ; Nita Dragoe Réf. : JOURNAL OF ALLOYS AND COMPOUNDS 508 (2010) 606-609 We demonstrate an all-silicon photodetector working at telecom wavelength. The device is a simple metalsemiconductor-metal detector fabricated on silicon-on-insulator. A two-dimensional photonic crystal nanocavity (Q = 60,000) is used to increase the response that arises from the linear and two-photon absorption of silicon. The responsivity of the detector is about 20 mA/W and its bandwidth is larger than 1 GHz. (C) 2010 Optical Society of America Electronic phase diagram of NdFe1-xRhxAsO Article publié en 2010 Auteurs : Berardan, D. Zhao, LD. Loreynne Loreynne Pinsard-Gaudart. Nita Dragoe Réf. : PHYSICAL REVIEW B 81 (2010) 094506 We report on the electrical resistivity, thermoelectric power, and electronic phase diagram of rhodium-doped NdFeAsO. Rhodium doping suppresses the structural phase transition and spin-density wave observed in the undoped material, and superconductivity emerges at x close to 0.05, despite the distortion of FeAs4 tetrahedra induced by the large size difference between Rh and Fe elements. The T-c (x) curve is domelike, and the highest T-c is reached at x=0.1, with T-c(onset)= 18 K. An upturn of the electrical resistivity above T-c has been observed, with a Kondo-type behavior above T-c and a Fermi- liquid behavior close to room temperature. Superconductivity at 15 K in NdFe0.9Rh0.1AsO without F-doping Article publié en 2010 Auteurs : Berardan, D. Zhao, LD. Loreynne Loreynne Pinsard-Gaudart. Nita Dragoe Réf. : PHYSICA C-SUPERCONDUCTIVITY AND ITS APPLICATIONS 470 (2010) 165-167 We present results of transport and magnetic properties measurements performed on polycrystalline NdFe0.9Rh0.1AsO. Despite the large size difference between Fe and Rh elements, this compound undergoes a superconducting transition with T-c similar to 15 K. We have compared the transport properties of this Rh-doped oxypnictide with that of optimally doped NdFeAsO0.88F0.12 Contrary to this latter compound, a strong upturn of the normal-state resistivity occurs above T-c, and no peak of the thermopower has been observed. (C) 2009 Elsevier B.V. All rights reserved. 28/02/2013 63