Publications

2004

• Photoconductivity and photoemission studies of diamond irradiated by ultrashort VUV pulses
  
  • Gaudin Jérôme
  • Geoffroy Ghita
  • Guizard Stéphane
  • Petite Guillaume
  • Klimentov Serguei M.
  • Garnov Serguei V.
  • Pivovarov Pavel A.
  • Carre Bertrand
  • Belsky Andrei
  • Martin Patrick
  Applied Physics B - Laser and Optics, Springer Verlag, 2004, 78, pp.1001.
• SPATIALLY PERIODIC STRUCTURES, UNDER FEMTOSECOND PULSED EXCITATION OF CRYSTALS
  
  • Petite Guillaume
  • Martynovitch Evgueni F.
  • Dresvianski Vladimir P.
  • Starchenko Anton A.
  Applied Physics Letters, American Institute of Physics, 2004, 84, pp.4550. Measuring the luminescence intensity of specially prepared irradiation defects induced in crystals, we observe that the longitudinal structure of quasi-interferences induced by two orthogonally polarized femtosecond pulses propagating together with different velocities is insensitive to the spatial broadening due to velocity dispersion in the crystals. On the contrary, it does depend on the pulse duration when it is changed by varying the spectral width of the radiation. It thus allows a direct measurement of the coherence time of such pulses. Stability of the axial selectivity is a good sign, taking away a number of serious limitations concerning possible applications.
• Amorphous vortex phase in Bi2Sr2CaCu2O8 after the first order liquid-solid phase transition
  
  • Menghini M.
  • Fasano Y.
  • de La Cruz F.
  • Banerjee S.S.
  • Myasoedov Y.
  • Zeldov E.
  • J. van Der Beek C.
  • Konczykowski M.
  • Tamegai T.
  Journal of Low Temperature Physics, Springer Verlag (Germany), 2004, 135, pp.139. It is widely accepted that the first-order vortex liquid-solid phase transition is associated with a crystalline solid phase and the second order transition with an amorphous one. The combination of a technique that determines the order of the transition with the visualization of the vortex structure has allowed the detection, for the first time, of a first-order liquid-solid transition without structural symmetry change. The results show that the quasi-long range order of the solid phase is not a necessary condition for the first-order phase transition to occur. This opens an important question on the microscopic origin of the liquid-solid phase transition in vortex matter
• b-irradiation in borosilicate glasses : the role of the mixed alkali effect
  
  • Ollier Nadège
  • Boizot Bruno
  • Reynard Bruno
  • Ghaleb Dominique
  • Petite Guillaume
  Nuclear Instruments and Methods in Physics Research Section B: Beam Interactions with Materials and Atoms, Elsevier, 2004, 218, pp.176-182.
• Porous vortex matter
  
  • Banerjee S.S.
  • Zeldov E.
  • Soibel A.
  • Myasoedov Y.
  • Rappaport M.
  • Menghini M.
  • Fasano Y.
  • de La Cruz F.
  • J. van Der Beek C.
  • Konczykowski M.
  • Tamegai T.
  Physica C: Superconductivity and its Applications, Elsevier, 2004, 408, pp.495. Structure, dynamics, and thermodynamic properties of vortex matter in the presence of a low density of columnar defects (CDs) were studied in BSCCO crystals. Magnetic decorations show that when vortices outnumber CDs a heterogeneous vortex matter is formed consisting of two populations of vortices: vortices residing on CDs form a matrix of pinned vortices, whereas the interstitial vortices form ordered crystallites within the 'pores' of the matrix. Differential magneto-optical studies reveal that at elevated fields this porous phase melts in two stages, a first-order melting of the crystallites at a temperature considerably higher than the pristine melting, and a continuous melting of the matrix at still higher temperature. At low fields the two transitions occur simultaneously, giving rise to a sharp kink in the observed melting line
• Superconducting pinning by magnetic domains in a ferromagnet-superconductor bilayer
  
  • Z. Cieplak M.
  • Adamus Z.
  • Konczykowski M.
  • M. Chen X.
  • Byczuk A.
  • Abal'Oshev A.
  • Sang H.
  • L. Chien C.
  Acta Physica Polonica A, Polish Academy of Sciences. Institute of Physics, 2004, 106, pp.693. The local flux profile and the critical current are studied using an array of Hall sensors in a ferromagnetic-superconducting bilayer which consists of niobium film covering ferromagnetic Co/Pt multilayer with perpendicular magnetic anisotropy. The results indicate about threefold enhancement of the flux pinning in niobium layer caused by the isolated magnetic domains which are created during the magnetization reversal of the Co/Pt multilayer. The geometrical barrier is absent, and the critical current is strongly peaked in close vicinity to the sample center, suggesting that the critical state differs from that predicted by the Bean model
• Vortex Phase Diagram in Bi2Sr2CaCu2O8+$\delta$ with Damage Tracks Created by 30 MeV Fullerene Irradiation
  
  • Ishikawa N.
  • van der Beek C. J.
  • Dunlop A.
  • Jaskierowicz G.
  • Li Ming
  • Kes P. H.
  • Della-Negra S.
  Journal of the Physical Society of Japan, Physical Society of Japan 日本物理学会, 2004, 73, pp.2813-2821. Using 30 MeV C60 fullerene irradiation, we have produced latent tracks of diameter 20 nm and length 200 nm, near the surface of single crystalline Bi2Sr2CaCu2O8+δ. A preliminary transmission electron microscopy study shows evidence for a very high density of deposited energy, and the ejection of material from the track core in very thin specimens. The latent tracks reveal themselves to be exceptionally strong pinning centers for vortices in the superconducting mixed state. Both the critical current density and magnetic irreversibility line are significantly enhanced. The irradiated crystals present salient features of the (B,T) phase diagram of vortex matter both of pristine crystals, such as the first order vortex phase transition, and the exponential Bose-glass line characteristic of heavy ion-irradiated crystals. We show that the latter is manifestly independent of the pinning potential (10.1143/JPSJ.73.2813)
  DOI : 10.1143/JPSJ.73.2813
• Neural correlates of implicit object identification.
  
  • Pins D.
  • Meyer M. E.
  • Foucher J.
  • Humphreys G.
  • Boucart M.
  Neuropsychologia, Elsevier, 2004, 42 (9), pp.1247-59. The present study sought to assess neural correlates of implicit identification of objects by means of fMRI, using tasks that require matching of the physical properties of objects. Behavioural data suggests that there is automatic access to object identity when observers attend to a physical property of the form of an object (e.g. the object's orientation) and no evidence for semantic processing when subjects attend to colour. We evaluated whether, in addition to neural areas associated with decisions to specific perceptual properties, areas associated with access to semantic information were activated when tasks demanded processing of the global configuration of pictures. We used two perceptual matching tasks based on the global orientation or on the colour of line drawings. Our results confirmed behavioural data. Activations in the inferior occipital cortex, fusiform and inferior temporal gyri in both tasks (orientation and colour) account for perceptual and structural processing involved in each task. In contrast, activations in the posterior and medial parts of the fusiform gyrus, shown to be involved in explicit semantic judgements, were more pronounced in the orientation-matching task, suggesting that semantic information from the pictures is processed in an implicit way even when not required by the task. Thus, this study suggests that cortical regions usually involved in explicit semantic processing are also activated when implicit processing of objects occurs. (10.1016/j.neuropsychologia.2004.01.005)
  DOI : 10.1016/j.neuropsychologia.2004.01.005
• Potentialities of GaN-based microcavities in strong coupling regime at room temperature.
  
  • Ollier N.
  • Natali F.
  • Byrne D.
  • Disseix Pierre
  • Vasson A.
  • Leymarie Joël
  • Semond F.
  • Massies J.
  Superlattices and Microstructures, Elsevier, 2004, 34 (4-6), pp.599-606. In a recent publication [N. Antoine-Vincent, F. Natali, D. Byrne, A. Vasson, P. Disseix, J. Leymarie, M. Leroux, F. Semond, J. Massies, Phys. Rev. B 68 (2003) 153313], we have highlighted for the first time the exciton–photon strong coupling in a GaN-based microcavity and obtained a Rabi splitting of 31 meV persistent at 77 K. Our aim is now to study the feasibility of GaN-based microcavities for which the strong coupling regime would be maintained at room temperature. A complex heterostructure containing GaN/AlGaN quantum wells (QWs) is investigated by photoreflectivity and reflectivity at 5 K. The QW thickness is 3 nm and the Al composition and thickness of the barriers are respectively 0.11 and 10 nm. From the modeling of the experimental spectra, the values of the oscillator strength, the energy and the broadening parameter of the QW fundamental transition are determined; the broadening is found to be relatively weak (15 meV). Simulations of microcavities containing QWs have then been performed including this set of parameters: a theoretical Rabi splitting of 34 meV is obtained at 5 K. Considering an additional broadening induced by the increase of the temperature (23 meV), the strong coupling regime could be maintained theoretically at room temperature in such a structure. This is due to the low value of the inhomogeneous broadening related to the QW transition which is lower than in bulk GaN. The influence of the QW number and the nature of the Bragg mirror on the Rabi splitting is then discussed in realistic structures. (10.1016/j.spmi.2004.09.017)
  DOI : 10.1016/j.spmi.2004.09.017
• Optical absorption and electron energy loss spectra of carbon and boron nitride nanotubes: a first-principles approach
  
  • G. Marinopoulos A.
  • Wirtz L.
  • Marini A.
  • Olevano Valério
  • Rubio A.
  • Reining L.
  Applied physics. A, Materials science & processing, Springer Verlag, 2004, 78, pp.1157. We present results for the optical absorption spectra of small-diameter single-walled carbon and boron nitride nanotubes obtained by ab initio calculations in the framework of time-dependent density-functional theory. We compare the results with those obtained for the corresponding layered structures, i.e. the graphene and hexagonal boron nitride sheets. In particular, we focus on the role of depolarization effects, anisotropies, and interactions in the excited states. We show that the random phase approximation reproduces well the main features of the spectra when crystal local field effects are correctly included, and discuss to what extent the calculations can be further simplified by extrapolating results obtained for the layered systems to results expected for the tubes. The present results are relevant for the interpretation of data obtained by recent experimental tools for nanotube characterization, such as optical and fluorescence spectroscopies, as well as polarized resonant Raman scattering spectroscopy. We also address electron energy loss spectra in the small-q momentum-transfer limit. In this case, the interlayer and intertube interactions play an enhanced role with respect to optical spectroscopy
• Ab initio and semiempirical dielectric response of superlattices
  
  • Botti Silvana
  • Vast Nathalie
  • Reining Lucia
  • Olevano Valério
  • Claudio Andreani Lucio
  Physical Review B: Condensed Matter and Materials Physics (1998-2015), American Physical Society, 2004, 70, pp.045301. We present a study of the dielectric response of (GaAs)p∕(AlAs)p (001) superlattices in a wide range of barrier and well widths. We applied density functional theory and a semiempirical method to obtain the superlattice band structures. These were then used as a starting point to evaluate the optical spectra and macroscopic dielectric constants using time-dependent density functional theory. In this context, we investigated the role of crystal local field effects in determining the anisotropy of the dielectric constants. Furthermore, we calculated absorption spectra including the strong continuum excitonic effect through the use of an appropriate model exchange-correlation kernel. We analyzed in detail the complementarity of the ab initio and semiempirical approaches and we compared the successes and limitations of the different approximation schemes. (10.1103/PhysRevB.70.045301)
  DOI : 10.1103/PhysRevB.70.045301
• A structural approach by MAS NMR spectroscopy of mechanisms occurring under β-irradiation in mixed alkali aluminoborosilicate glasses
  
  • Ollier Nadège
  • Charpentier Thibault
  • Boizot Bruno
  • Petite Guillaume
  Journal of Physics: Condensed Matter, IOP Publishing [1989-....], 2004, 16, pp.7625-7635. Two series of mixed Na/K and Na/Li aluminoborosilicate glasses have been irradiated with electrons of 1.8 MeV at doses close to 109 Gy. Si, B and Al glass former environment changes under irradiation have been probed by MAS NMR spectroscopy. It was shown that the mixed alkali effect acts on the middle range compositions by operating with a selective blockage in irradiated glasses, depending on the alkali nature and concerning either modifier or charge compensator alkalis.
• 111. Observation of high energy photoelectrons from solids at moderate laser intensity
  
  • Belsky Andrei
  • Bachau Henri
  • Gaudin Jérôme
  • Geoffroy Ghita
  • Guizard Stéphane
  • Martin Patrick
  • Petite Guillaume
  • Philippov A.
  • Vassil'Ev Andrei N.
  • Yatsenko Boris
  Applied Physics B - Laser and Optics, Springer Verlag, 2004, 78, pp.989-994.
• Heating of Conduction Band Electrons by Intense Femtosecond Laser Pulses
  
  • Belsky Andrei
  • Martin Patrick
  • Bachau Henri
  • Vassiliev A.N.
  • Yatsenko Boris
  • Guizard Stéphane
  • Geoffroy Ghita
  • Petite Guillaume
  EPL - Europhysics Letters, European Physical Society / EDP Sciences / Società Italiana di Fisica / IOP Publishing, 2004, 67, pp.301-306.
• Dynamics of Femtosecond Laser Interactions with Dielectrics
  
  • Mao S.S.
  • Quéré Fabien
  • Guizard Stéphane
  • Mao X. L.
  • Russo R. E.
  • Petite Guillaume
  • Martin Philippe
  Applied physics. A, Materials science & processing, Springer Verlag, 2004, 79 (7), pp.1695. Femtosecond laser pulses appear as an emerging and promising tool for processing wide band-gap dielectric materials for a variety of applications. This article aims to provide an overview of recent progress in understanding the fundamental physics of femtosecond laser interactions with dielectrics that may have the potential for innovative materials applications. The focus of the overview is the dynamics of femtosecond laser-excited carriers and the propagation of femtosecond laser pulses inside dielectric materials.
• Exactly solvable models : a solution to different problems of laser matter interaction
  
  • Petite Guillaume
  • Shvartsburg Alexander
  , 2004, pp.11-20. With the increasing use of ultrashort laser pulses and nanoscale-materials, one is regularly confronted to situations in which the properties of the media supporting propagation are not varying slowly with time (or space). Hence, the usual WKB-type approximations fail, and one has to resort to numerical treatments of the problems, with a considerable loss in our insight into the physics of laser-matter interaction. We will present a new approach which allows a fully analytical solution of such problems, based on a transformation of the propagation equations into a new space where phase accumulation is linear with either time or space, which greatly simplifies their treatment. Though this method is restricted to some special models of the time or space varying dielectric constant, those are however general enough to encompass practically all experimental situations. It allows to introduce the concept of "non-stationarity induced" (or "inhomogeneity induced") dispersion. We will analyse the problem of reflection and propagation in two types of media whose dielectric constant vary rapidly at either the laser period or the laser wavelength scale. Extension of such techniques to the case of arbitrarily high non linearities will be considered too.
• Flux lenses in the crossing lattices regime of layered superconductors
  
  • Cole D.
  • Crisan A.
  • J. Bending S.
  • Tamegai T.
  • van Der Beek K.
  • Konczykowski M.
  Physica C: Superconductivity and its Applications, Elsevier, 2004, 404, pp.99. We report here measurements of flux lensing behaviour which have been performed on Bi2Sr2CaCu2O8+delta single crystals placed on top of linear Hall probe arrays. In the crossing lattices regime we observe significant flux focussing as the in-plane field is swept up with a small constant density of pancake vortices. We also observe a sharp discontinous lock-in feature in local magnetic induction when the net field is close to the a-b plane
• Detailed analysis of the segregation driving forces for Ni(Ag) and Ag(Ni) in the sigma = 11{113} and sigma = 11{332} grain boundaries
  
  • Lezzar B.
  • Khalfallah O.
  • Larere A.
  • Paidar V.
  • Hardouin Duparc Olivier
  Acta Materialia, Elsevier, 2004, 52, pp.2809. The behaviour with respect to segregation is studied for two qualitatively different symmetrical tilt grain boundaries (GBs): a low energy boundary with mirror-symmetric structure on the {1 1 3} plane and the high energy {3 3 2} GB with a "zigzag" structural pattern. These two structures have been confirmed by high resolution transmission electronic microscopy observations in nickel. Intergranular segregation is studied in the limit of infinitely diluted solution for Ni(Ag) and Ag(Ni) systems modelled with Finnis–Sinclair like potentials. The atomic sites are characterized by a geometrical parameter defined by their exact Voronoy volumes and the pressure locally exerted. The segregation energies and driving forces are compared with these parameters in order to characterize a segregation "susceptibility" of intergranular atomic sites. The size effect calculated by the method of virtual impurity represents the main segregation driving force for the considered systems
• Transport properties and magnetic domain structure in low-doped LaCaMnO manganite single crystals
  
  • Jung G.
  • Markovich V.
  • Yuzhelevski Y.
  • Indenbom M.
  • J. van Der Beek C.
  • Mogilyanski D.
  • M. Mukovskii Y.
  Journal of Magnetism and Magnetic Materials, Elsevier, 2004, 272, pp.1800. The low temperature resistivity up-turn in lightly Ca doped LaCaMnO single crystals has been attributed to the domination of the tunneling mechanism in low temperature transport. The intrinsic tunnel barriers have been associated with spontaneous ferromagnetic domains walls. The magneto-optical technique has been employed to observe the relevant domain structure. A regular network of spontaneous ferromagnetic domains undergoes significant changes resulting in apparent rotation of the domain walls in the temperature range coinciding with the resistivity up-turn
• Electron acceleration by surface plasma waves in the interaction between femtosecond laser pulses and sharp-edged overdense plasmas
  
  • Kupersztych J
  • Raynaud M
  • Riconda C
  Physics of Plasmas, American Institute of Physics, 2004. The relativistic acceleration of electrons by the field of surface plasma waves created in the interaction between ultrashort high-intensity laser pulses with sharp-edged overdense plasmas has been investigated. It is shown that the initial phase of the wave experienced by the electrons play a leading part by yielding a well-defined peaked structure in the energy distribution function. This study suggests that resonant excitation of surface plasma waves could result in quasi-monokinetic energetic electron bunches. When the space charge field becomes too strong, this mechanism can evolve toward a true absorption process of the surface wave energy via an enhanced ''vacuum heating'' mechanism generalized to the case of surface plasma waves. (10.1063/1.1650353͔)
  DOI : 10.1063/1.1650353͔
• Optical anisotropy induced by cesium adsorption on the As-rich c(2X8) reconstruction of GaAs(001)
  
  • Hogan C.
  • Paget D.
  • E. Tereshchenko O.
  • Reining L.
  • Onida G.
  Physical Review B: Condensed Matter and Materials Physics (1998-2015), American Physical Society, 2004, 6912, pp.5332. Upon adsorption of Cs, the As-rich c(2 X 8)/(2 X 4) reconstruction of GaAs(001) is found to exhibit an intense negative signal between 3 eV and 5 eV in the reflectance anisotropy spectrum. This signal has a universal character in that similar features also appear on the Ga-rich surface. The mechanism of this signal is interpreted using ab initio calculations of Cs adsorption at As and Ga sites of the As-rich surface. The calculations succeed in explaining the universality of the signal. In the vicinity of the E-0' bulk critical point at 4.5 eV, the signal arises from perturbation of bulk states terminating at the surface. At lower energies, the signal arises from the creation of new surface resonances induced by the Cs adatom
• Transition from Bose Glass to Normal State in the (K,Ba)BiO3 Superconductor
  
  • Klein T.
  • Marcenat C.
  • Blanchard S.
  • Marcus J.
  • Bourbonnais C.
  • Brusetti R.
  • J. van Der Beek C.
  • Konczykowski M.
  Physical Review Letters, American Physical Society, 2004, 92, pp.037005. The introduction of columnar defects in (K,Ba)BiO3 single crystals shifts both the irreversibility and thermodynamic transition lines, respectively, deduced from ac susceptibility (and/or transport) and specific heat measurements, upwards. This shift can be attributed to the defect-induced decrease of the difference (F) between the free energies in the superconducting and the normal states, assuming that the position of the superconducting transition is given by the condition |F|kBT/3. This criterion also perfectly reproduces the influence of the angle between the tracks and the external field. This result suggests that no vortex liquid phase exists in this system
• Spin-dependent magnetoresistance in multiwall carbon nanotubes
  
  • Hoffer X.
  • Klinke C.
  • M. Bonard J.
  • Gravier L.
  • E. Wegrowe J.
  EPL - Europhysics Letters, European Physical Society / EDP Sciences / Società Italiana di Fisica / IOP Publishing, 2004, 67, pp.103. The spin-dependent transport in multiwall carbon nanotubes, obtained by chemical vapour deposition in porous alumina membranes, has been investigated. The zero-bias anomaly is shown to follow the typical power law GT(-alpha) (eV/kT). In the nanotubes contacted with Ni pads, the magnetoresistance due to the spin-polarised current (SD-MR) is destroyed. In the case of those contacted with Co pads, however, the SD-MR is observed. These measurements show that both the observation of a typical scaling law of the conductance (for nanotubes tip to 1.5 mum) and a short spin diffusion length (less than 0.15 mum with nickel contacts and 0.7 mum with cobalt contacts) coexist through the nanotube. This observation may be interpreted in terms of a reminiscence of the Luttinger-liquid behaviour with spin-charge separation
• beta irradiation borosilicate glasses: the role of the mixed alkali effect
  
  • Lyard L.
  • Klein T.
  • Marcus J.
  • Brusetti R.
  • Marcenat C.
  • Konczykowski M.
  • Mosser V.
  • H. Kim K.
  • W. Kang B.
  • S. Lee H.
  • I. Lee S.
  Nuclear Instruments and Methods in Physics Research Section B: Beam Interactions with Materials and Atoms, Elsevier, 2004, 218, pp.176. The first penetration field (H-p) has been deduced from local magnetization and specific heat measurements in magnesium diboride single crystals. For H-a(parallel toc), the geometrical barriers (GB) play a dominant role in the irreversibility mechanism. In thin samples, neglecting the GB in this direction would then lead to a large overestimation of H-c1 deduced from H-p through the standard elliptical formula. The lower critical field is found to be isotropic at low temperature (similar to0.11+/-0.01 T).
• Observation of high energy photoelectrons from solids at moderate laser intensity
  
  • N. Belsky A.
  • Bachau H.
  • Gaudin J.
  • Geoffroy G.
  • Guizard S.
  • Martin P.
  • Petite G.
  • Philippov A.
  • Vasil'Ev A.N.
  • N. Yatsenko B.
  Applied Physics B - Laser and Optics, Springer Verlag, 2004, 78, pp.989. We investigate the photoemission for a set of wide band-gap crystals irradiated by femtosecond Ti-Sapphire laser pulses at intensities varying from 0.5 to 6 TW/cm(2) (below the optical breakdown threshold). The measured total electron yield increases linearly with the laser intensity in this intensity range. An intense and wide plateau of high energy electrons appears in the photoelectron spectra at excitation intensities larger than 1 TW/cm(2). The exponential cut-off of this plateau reaches 40 eV at maximal applied intensities. In order to explain such a behavior, we propose a mechanism where the heating is due to a sequence of direct interbranch one- and multi-photon transitions in the conduction band