Publications

2004

• 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.
• 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
• 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
• Electronic structure and electron energy-loss spectroscopy of ZrO2 zirconia
  
  • K. Dash L.
  • Vast N.
  • Baranek P.
  • C. Cheynet M.
  • Reining L.
  Physical Review B: Condensed Matter and Materials Physics (1998-2015), American Physical Society, 2004, 70, pp.245116. The atomic and electronic structures of zirconia are calculated within density functional theory, and their evolution is analyzed as the crystal-field symmetry changes from tetrahedral [cubic (c-ZrO2) and tetragonal (t-ZrO2) phases] to octahedral (hypothetical rutile ZrO2), to a mixing of these symmetries (monoclinic phase, m-ZrO2). We find that the theoretical bulk modulus in c-ZrO2 is 30% larger than the experimental value, showing that the introduction of yttria in zirconia has a significant effect. Electronic structure fingerprints which characterize each phase from their electronic spectra are identified. We have carried out electron energy-loss spectroscopy experiments at low momentum transfer and compared these results to the theoretical spectra calculated within the random phase approximation. We show a dependence of the valence and 4p (N2,3 edge) plasmons on the crystal structure, the dependence of the latter being brought into the spectra by local-field effects. Last, we attribute low energy excitations observed in EELS of m-ZrO2 to defect states 2 eV above the top of the intrinsic valence band, and the EELS fundamental band gap value is reconciled with the 5.2 or 5.8 eV gaps determined by vacuum ultraviolet spectroscopy
• Persistence of the intrinsic transition in the vortex matter of disordered BSCCO:2212 crystals
  
  • Konczykowski M.
  • J. van Der Beek C.
  • Zeldov E.
  • Ming Li.
  • H. Kes P.
  Physica C: Superconductivity and its Applications, Elsevier, 2004, 408, pp.547. The first order melting transition (FOT) in vortex matter of clean Bi2Sr2CaCu2O8 crystals, is identified by a discontinuity in the reversible magnetization, which extends to the low temperature (irreversible) regime in the form of a jump in the energy barrier vs. current, U(J), variation. Heavy ion irradiation disorders the vortex lattice, enhances flux pinning, and is believed to suppress the FOT. However, in underdoped samples, detailed measurements of magnetic relaxation by the Hall-array technique reveal the existence of a discontinuous jump in the U(J) curve precisely at the location of FOT of pristine crystals
• 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
• 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
• 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
• Local crystallization induced in Fe-based amorphous alloys by swift heavy projectiles
  
  • Rizza G.
  • Dunlop A.
  • Jaskierowicz G.
  • Kopcewicz M.
  Nuclear Instruments and Methods in Physics Research, North-Holland ; Elsevier [1981-1984], 2004, 226, pp.609-621. We report the effect of the high density of electronic excitation deposited along the path of swift heavy ions in various amorphous alloys. The samples were irradiated at low temperature with GeV Pb ions up to fluences of 1 × 1011 to 2.3 × 1013 cm−2. The formation of nanocrystalline phases was observed by transmission electron microscopy in the FINEMET-like Fe73.5Nb4.5Cr5Cu1B16 alloy and in the NANOPERM ternary Fe90Zr7B3 glassy systems but not in the Fe80.5Nb7B12.5 alloy. The crystallization phenomenon was interpreted in terms of the relaxation of the high level of energy deposited in electronic excitations along the path of Pb ions in the target, which induce radial pressure waves in the vicinity of the projectile trajectories. These mechanical stresses destabilize the amorphous structure and induce nanocrystallization
• Applications of Time-Dependent Density Functional Theory
  
  • Botti Silvana
  Physica Scripta, IOP Publishing, 2004, T109, pp.54. The progress of experimental techniques makes more and more precise measurements available. Their interpretation requires improved theoretical tools. The time-dependent density functional theory (TDDFT) allows to study electronic excitations involved in spectroscopic experiments, possibly conserving a computational effort comparable to that of ground-state density functional theory. I will present some applications of TDDFT to the calculation of absorption and electron energy loss spectra in extended and finite systems, discussing the advantages and the limits of different approximation schemes. (10.1238/Physica.Topical.109a00054)
  DOI : 10.1238/Physica.Topical.109a00054
• Raman investigation of structural changes induced by e-beam irradiation in Ge doped silica MCVD glasses
  
  • S. Jacqueline A.
  • Poumellec B.
  • C. Chervin J.
  • Garcia-Blanco S.
  • Esnouf S.
  Materials Science and Engineering: B, Elsevier, 2004, 107, pp.46. Microstructural changes of germanium (Ge)-doped silica glasses irradiated with electron beam (e-beam) have been investigated by Raman spectroscopy. Two mechanisms correlated to the specific volume changes induced by e-beam irradiation were observed by surface topography measurement. As we have previously demonstrated, they depend on the Ge content and the irradiation dose. The compaction of the structure (which decreases with the Ge concentration) is attributed to an increase of the three and four-membered ring species which is maximal at the surface and decreases with depth. By means of Monte-Carlo simulations, we have correlated the energy deposition with the compaction process. Some specific Raman components are attributed to the expansion of the structure observed for high Ge content and high irradiation dose. In this case, an increase of the anti-symmetric stretching modes of the bridging oxygen in the Si---O---Ge and Si---O---Si groups are observed at the surface
• Long- and short-range magnetic order charge transfer, and superconductivity in Yba2Cu3 -xCOxO7
  
  • Maury F.
  • Mirebeau I.
  • A. Hodges J.
  • Bourges P.
  • Sidis Yvan
  • Forget A.
  Physical Review B: Condensed Matter and Materials Physics (1998-2015), American Physical Society, 2004, 69, pp.094506. We have performed powder-neutron-diffraction measurements in YBa2Cu3–xCoxO7 for a large range of Co concentrations (x = 0.04–0.72) and determined the magnetic phase diagram. As previously observed, superconductivity disappears for x0.42 and antiferromagnetic long-range order emerges above this value. The antiferromagnetic order shows noticeable differences compared to that in unsubstituted YBa2Cu3O6 + and surprisingly survives to a much higher hole doping. In contrast to recent results in YBa2Cu3–xCoxO7 single crystals, there is no evidence of any long-range antiferromagnetic order in the superconducting phase. The Co valence evolves from 4+ to 3+ with increasing Co concentration. We studied the short-range chemical and magnetic correlations between the Co ions in superconducting (x0.36) and antiferromagnetic (x0.42) samples. The Co ions predominantly occupy the Cu1 sites and their moments remain mostly disordered, forming random antiferromagnetic next nearest neighbor pairs, which compete with the long-range order. This can explain the low value for the ordered Cu1 site moment
• 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.
• 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.
• 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.
• 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
• 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.
• 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
• 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
• 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.
• 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
• 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
• Swift heavy ion induced graft polymerization in track etched membranes' submicroscopic pores
  
  • Mazzei R.
  • García Bermúdez G.
  • Betz N.
  • Cabanillas E.
  Nuclear Instruments and Methods in Physics Research Section B: Beam Interactions with Materials and Atoms, Elsevier, 2004, 226, pp.575. Cl or Pb irradiated foils of poly(vinylidene fluoride) (PVDF) were chemically etched to produce nuclear track membranes (NTM) with submicroscopic pores. The NTM were grafted with styrene using the remaining active sites produced by the heavy ion beams. Experimental curves of grafting yield were measured by weight difference as a function of ion fluence and etching time. As the etching time was increased from 0 to 30 min a decrease of the grafting yield was observed. Grafted foils were also analysed by Fourier transform infrared spectroscopy (FTIR). Both measurements suggest that the styrene was grafted on the pore wall of the NTM using the active sites left by the ion beam