Publications

2005

• PHOTOCONDUCTIVITY AND PHOTOEMISSION OF DIAMOND UNDER FEMTOSECOND VUV IRRADIATION
  
  • Gaudin Jérôme
  • Geoffroy Ghita
  • Guizard Stéphane
  • Olevano Valério
  • Esnouf Stéphane
  • Klimentov Serguei M.
  • Pivovarov Pavel A.
  • Garnov Serguei V.
  • Martin Patrick
  • Belsky Andrei
  • Petite Guillaume
  , 2005. In order to gain some insight on the electronic relaxation mechanisms occuring in diamond under high intensity laser excitation and/or VUV excitation, we studied experimentally the pulsed conductivity induced by femtosecond VUV pulses, as well as the energy spectra of the photoelectrons released by the same irradiation. The source of irradiation consists in highly coherent VUV pulses obtained through high order harmonic generation of a high intensity femtosecond pulse at a 1.55 eV photon energy (titanium-doped sapphire laser). Harmonics H9 to H17 have been used for photoconductivity (PC) and harmonics H13 to H27 for photoemission experiments (PES). As the photon energy is increased, it is expected that the high energy photoelectrons will generate secondary e-h pairs, thus increasing the excitation density and consequently the PC signal. This is not what we observe : the PC signal first increases for H9 to H13, but then saturates and even decreases. Production of low energy secondary e-h pairs should also be observed in the PES spectrum. In fact we observe very few low energy electrons in the PES spectrum obtained with H13 and H15, despite the sufficient energy of the generated free carriers. At the other end (H21 and above), a very intense low energy secondary electron peak is observed. As a help to interprete such data, we realized the first ab initio calculations of the electronic lifetime of quasiparticles, in the GW approximation in a number of dielectrics including diamond. We find that the results are quite close to a simple "Fermi-liquid" estimation using the electronic density of diamond. We propose that a quite efficient mechanism could be the excitation of plasmons by high energy electrons, followed by the relaxation of plasmons into individual e-h pairs.
• Characterization of carbon and iron nanostructures synthesized by the DC arc discharge method: influence of the location in the reactor and of the pressure
  
  • Fnidiki Abdeslem
  • Lemarchand Dany
  • Talbot Etienne
  • Pascard H.
  European Physical Journal: Applied Physics, EDP Sciences, 2005, 32 (3), pp.177-185. X-ray diffraction, Mössbauer spectroscopy, Scanning Electron Microscopy (SEM) and Transmission Electron Microscopy (TEM) techniques were used to characterize the Fe-C phases in the soots synthesized by the DC arc discharge method. Various equilibrium and non-equilibrium Fe-C compounds were identified, with fractions depending on both the location in the reactor and the helium gas pressure. The soots obtained are composed of the same five phases (C-graphite, α-Fe, γ-Fe, Fe3C and Fe5C2) whatever the helium gas pressure and wherever they are situated in the reactor. However, the location in the reactor has a considerable influence on the size of the particles in the nanostructure. The Fe-C compounds in the Pyrex vessel samples (CL) seem only to be present in the form of nanoparticles embedded in an amorphous gangue, while the water-cooled copper cylinder samples (RS) contain, in addition to these nanoparticles, large composite crystalline particles. (10.1051/epjap:2005094)
  DOI : 10.1051/epjap:2005094
• Thermodynamics of the vortex liquid in heavy-ion-irradiated superconductors
  
  • J. van Der Beek Cornelis
  • Konczykowski Marcin
  • Fruchter Luc
  • Brusettii René
  • Klein Thierry
  • Marcus Jacques
  • Marcenat C.
  Physical Review B: Condensed Matter and Materials Physics (1998-2015), American Physical Society, 2005, 72, pp.214504. It is shown that the large effect of heavy ion irradiation on the thermodynamical properties of the anisotropic superconductor YBa2Cu3O7− extends well into the superconducting fluctuation regime. The presence of the induced amorphous columnar defects shifts the specific-heat maximum at the normal-to-superconducting transition. This effect is similar to that recently put into evidence in cubic KxBa1−xBiO3 x 0.35 . In both compounds, vortex pinning manifests itself as a sharp angular dependence of the equilibrium torque. In YBa2Cu3O7− , pinning by the defects appears at the temperature TCp max of the specific-heat maximum, well above the magnetic irreversibility line Tirr H . In isotropic KxBa1−xBiO3, the onset of the pinning-related torque anomaly tracks the onset of the specific-heat anomaly and the irreversibility line. In YBa2Cu3O7− , fluctuations of the amplitude of the order parameter and not vortex line wandering are ultimately responsible for the vanishing of pinning. In KxBa1−xBiO3, vortex pinning disappears only at the superconducting-to-normal transition. The results indicate that in both compounds, the pinning energy at the "Bose-glass" transition is large with respect to the total free energy gain in the superconducting state. By implication, the mechanism of this latter transition should be reconsidered. (10.1103/PhysRevB.72.214504)
  DOI : 10.1103/PhysRevB.72.214504
• Processus électroniques d'excitation et de relaxation dans les solides diélectriques excités par des impulsions ir et xuv ultracourtes
  
  • Gaudin Jerome
  , 2005. Nous avons étudiés l'excitation d'un solide diélectrique par une impulsion laser femtoseconde (fs) intense dans le domaine visible où XUV. Ce type d'irradiation produit des électrons excit és avec des énergies initiales qui vont de quelques eV à quelques dizaines d'eV au dessus du bas de la bande de conduction. La relaxation de ces électrons est à l'origine de nombreux phénomènes tels que l'ablation laser, le claquage optique ou le transport des électrons " chauds " dans les matériaux à intérêt technologique (SiO2 et diamant). L'objectif de ce travail de thèse est d'étudier de façon directe et de mieux comprendre ces mécanismes de relaxation électroniques. Deux techniques expérimentales complémentaires, utilisant les impulsions XUV ultrabrèves, issues de la génération d'harmoniques d'ordres élevés, ont été mises oeuvre pour mener à bien ces études. Tout d'abord, les expériences de photoémission ont permis de mettre en lumière un nouveau mécanisme d'absorption du rayonnement par les électrons de la bande de conduction : les transitions multiphotoniques interbandes. Nos résultats montrent que ce processus est le mécanisme dominant d'échauffement des électrons. Cette conclusion est de plus corroborée par les résultats d'un modèle théorique basé sur la résolution de l'équation de Schrödinger dépendante du temps. D'autre part, des expériences " pompe/sonde " de photoémission résolue en temps ont eu pour but de sonder la population d'électrons excités par une impulsion XUV et de suivre son évolution temporelle sur une échelle de temps fs à ps. Les temps de décroissance mesurés sont de l'ordre de quelques ps pour des électrons de 30 eV. L'interprétation des ces durées de vie longue est problématique. Nous suggérons un modèle de relaxation en deux étapes, tout d'abord purement électronique et rapide, puis d'interaction avec le réseau plus lente, pour expliquer ces résultats expérimentaux. Le second type d'expériences porte sur une spectroscopie de photoconduction sur du diamant. En utilisant les harmoniques d'ordres élevés comme source d'excitation nous avons mesuré le courant de déplacement induit qui permet d'accéder au nombre d'électrons excités en fonction de l'énergie des photons incidents. Cette information permet d'étudier l'efficacité de l'ionisation par impact (collision inélastique électron/électron). Nos résultats peuvent s'interpréter par la structure particulière du diamant qui comporte une deuxième bande interdite 10 eV au dessus du bas de la bande de conduction. Des simulations Monte-Carlo permettent de confirmer cette interprétation.
• Echange et Corrélation dans la Structure Electronique des Solides, du Silicium à l'Oxyde Cuivreux: Approximation GW et au-delà
  
  • Bruneval F.
  , 2005. La structure électronique des cristaux est un nom polymorphe qui couvre une large gamme de propriétés des électrons dans les solides périodiques. Par exemple, il peut se référer à la probabilité de trouver un électron au point r de l'espace, en d'autres termes, à la densité électronique. Il peut faire référence à l'énergie nécessaire pour extraire un électron du matériau, l'énergie d'ionisation, ou encore, le gain énergétique lorsqu'un électron est ajouté au système, l'affinité électronique. Il peut aussi se lire la réponse des électrons du solide à une perturbation externe (un photon ou un électron rapide). Toutes ces propriétés caractérisent la structure électronique du solide. Ils décrivent les aspects bien différents. Certains d'entre eux sont propriétés de l'état, d'autres correspondent à des états excités. Certains d'entre eux de conserver le nombre de particules, d'autres pas. En conséquence, les propriétés qui sont généralement appelés «structure électronique» sont mesurées avec différentes configurations expérimentales, par exemple photoémission directe et inverse, l'absorption optique, de l'énergie d'électrons de perte ... Et de manière analogue, la description théorique et la prévision de ces propriétés requièrent cadres distincts. Ce travail de thèse se chargera de la question de la structure électronique de l'oxyde cuivreux, Cu2O. Par conséquent, différentes méthodes théoriques seront utilisées et les résultats seront comparés à un large éventail de techniques expérimentales.
• Peptide immobilization onto radiation grafted PVDF-g-poly(acrylic acid) films
  
  • Clochard M.-C
  • Betz N
  • Goncalves M
  • Bittencourt C
  • Pireaux J.-J
  • Gionnet K
  • Déléris G
  • Le Moël A
  Nuclear Instruments and Methods in Physics Research Section B: Beam Interactions with Materials and Atoms, Elsevier, 2005, 236, pp.208. Introducing hydrophilic functions on poly(vinylidene fluoride) (PVDF) films surface allows the covalent immobili-zation of peptides. Therefore radiation grafting of acrylic acid (AA) in pre-irradiated PVDF films was achieved to allow surface functionalization with linear and cyclic peptides. Peptides were bound via spacer molecules using EDC as a coupling agent. The reactions were followed by Fourier Transform Infrared (FTIR) spectroscopy in attenuated total reflection (ATR) mode. The amount of immobilized peptides was determined by UV spectroscopy. As well, an uncommon method for PVDF characterization and reactions quantification was used: high-resolution-magic angle spinning nuclear mass spectroscopy (HR-MAS NMR). Spacer saturation of the film surface corresponded to 25 mol% yield meaning that one spacer on 4 carboxylic acids was covalently bound. XPS experiments were also performed to deepen analysis of the surface composition. Peptide density is governed by steric hindrance. ELISA tests showed that the peptidesÕ activity is maintained. (10.1016/j.nimb.2005.04.029)
  DOI : 10.1016/j.nimb.2005.04.029
• Conformal anodic oxidation of aluminum thin films
  
  • Cojocaru C. S.
  • Padovani J.M.
  • Wade T.
  • Mandoli C.
  • Jaskierowicz G.
  • Wegrowe J. -E.
  • Morral A.F.I.
  • Pribat Didier
  Nano Letters, American Chemical Society, 2005, 5 (4), pp.675-680. Membrane-based synthesis, also called template synthesis, is a very general approach used to prepare arrays of nanomaterials with monodispersed geometrical features. The most commonly used porous templates are track-etched polycarbonate and porous anodic alumina membranes. Common to all these templates is the fact that the pores are perpendicular to the surface of the membrane. Here, a novel approach is presented, where the pores are synthesized parallel to the surface of the membrane. For the first time, the anodic oxidation of an aluminum thin film is performed laterally, i.e., parallel to the surface of the substrate, instead of perpendicular as usually done. For low anodic oxidation voltages (between 3 and 5 V) we obtain highly regular and ordered pore arrays, at least over a few hundred nanometers length, with a minimum pore size of similar to 3 to 4 nm. With such porous alumina structures, the controlled in-plane organization of arrays of template-grown nanowires and carbon nanotubes for reproducible device fabrication should be much easier. (10.1021/nl050079b)
  DOI : 10.1021/nl050079b
• Analysis of molecular oxygen formation in irradiated glasses: a Raman depth profile study
  
  • Ollier N.
  • Boizot B.
  • Reynard Bruno
  • Ghaleb D.
  • Petite G.
  Journal of Nuclear Materials, Elsevier, 2005, 340 (2-3), pp.209-213. Depth profiles experiments have been performed by Raman spectroscopy on three alkali (Na, Li, K) borosilicate glasses irradiated with 1.8 MeV electrons at 1 and 3 GGy. These experiments show that molecular oxygen produced under β irradiation is concentrated near the glass surface according to a depth depending on the irradiation dose. Moreover, we observed that the polymerisation increase is the same in the entire volume sample. The average Si–O–Si angle decrease under irradiation is also homogeneous in the whole irradiated glass volume. From all results, we demonstrate that oxygen migrates up to the glass surface during irradiation without strong interaction with the glass network. Migration of oxygen and probably alkalis takes place through percolation channels with a possible departure of oxygen in some cases. (10.1016/j.jnucmat.2004.11.011)
  DOI : 10.1016/j.jnucmat.2004.11.011
• Plasmon channels in the electronic relaxation of diamond under high-order harmonics femtosecond irradiation.
  
  • Belsky Andrei
  • Esnouf Stéphane
  • Garnov Serguei V.
  • Gaudin Jérôme
  • Geoffroy Ghita
  • Guizard Stéphane
  • Klimentov Serguei M.
  • Martin Patrick
  • Olevano Valério
  • Petite Guillaume
  • Pivovarov Pavel A.
  Laser Physics, MAIK Nauka/Interperiodica, 2005, Letters 2, pp.292-296. We used high order harmonics of a femtosecond titanium-doped sapphire system (pulse duration 25 fs) to realise Ultraviolet Photoelectron Spectroscopy (UPS) measurements on diamond. The UPS spectra were measured for harmonics in the range 13 to 27. We also made ab initio calculations of the electronic lifetime of conduction electrons in the energy range produced in the UPS experiment. Such calculations show that the lifetime suddenly diminishes when the conduction electron energy reaches the plasmon energy, whereas the UPS spectra show evidence in this range of a strong relaxation mechanism with an increased production of low energy secondary electrons. We propose that in this case the electronic relaxation proceeds in two steps : excitation of a plasmon by the high energy electron, the latter decaying into individual electron-hole pairs, as in the case of metals. This process is observed for the first time in an insulator and, on account of its high efficiency, should be introduced in the models of laser breakdown under high intensity. (10.1002/lapl.200510001)
  DOI : 10.1002/lapl.200510001
• Use of ion beam analysis techniques to characterise iron corrosion under water radiolysis
  
  • Lapuerta S.
  • Moncoffre N.
  • Millard-Pinard N.
  • Mendes E.
  • Corbel C.
  • Crusset D.
  Nuclear Instruments and Methods in Physics Research Section B: Beam Interactions with Materials and Atoms, Elsevier, 2005, 240, pp.288. The aim of this paper is to study the effect of water radiolysis under 12 MeV proton irradiation on the corrosion behaviour of pure iron. Oxygen and hydrogen playing a crucial role during the corrosion process have been specifically investigated. Heavy desaerated water ( enriched at 99.9% in D) was also used to determine the origin of hydrogen at the iron surface. Proton irradiations were performed at the CERI cyclotron in Orleans. Both sides of the Fe foil (respectively in contact with air and with water) were analysed with ion beam techniques: alpha Rutherford backscattering spectrometry was used to profile oxygen, elastic recoil detection analysis has allowed to profile hydrogen. The use of D2O gives evidence that the hydrogen concentration present on the water face could originate from wet air. In addition, in case of the aerated deionised H2O media, it is shown that the irradiation process induces a strong corrosion. Scanning electron microscopy experiments confirm the formation of oxide precipitates
• Effect of external gamma irradiation on dissolution of the spent UO2 fuel matrix
  
  • Jegou C.
  • Muzeau B.
  • Broudic V.
  • Peuget S.
  • Poulesquen A.
  • Roudil D.
  • Corbel C.
  Journal of Nuclear Materials, Elsevier, 2005, 341, pp.62. Leaching experiments were performed on UO2 pellets doped with alpha-emitters (Pu-238/239) and on spent fuel, in the presence of an external gamma irradiation source (A(60)Co = 260 Ci, D gamma = 650 Gy h(-1)). The effects of alpha, beta, gamma radiation, the fuel chemistry and the nature of the cover gas (aerated or Ar + 4%H-2) on water radiolysis and on oxidizing dissolution of the UO2 matrix are quantified and discussed. For the doped UO2 pellets, the nature of the cover gas clearly has a major role in the effect of gamma radiolysis. The uranium dissolution rate in an aerated medium is 83 mg m(-2) d(-1) compared with only 6 mg m-2 d-1 in Ar + 4%H-2. The rate drop is accompanied by a reduction of about four orders of magnitude in the hydrogen peroxide concentrations in the homogeneous solution. The uranium dissolution rates also underestimate the matrix alteration rate because of major precipitation phenomena at the UO2 pellet surface. The presence of studtite in particular was demonstrated in aerated media; this is consistent with the measured H2O2 concentrations (1.2 x 10(-4) mol L-1). For spent fuel, the presence of fission products (Cs and Sr), matrix alteration tracers, allowed us to determine the alteration rates under external gamma irradiation. The fission product release rates were higher by a factor of 5-10 than those of the actinides (80-90% of the actinides precipitated on the surface of the fragments) and also depended to a large extent on the nature of the cover gas. No significant effect of the fuel chemistry compared with UO2 was observed on uranium dissolution and H2O2 production in the presence of the 6 Co source in aerated conditions. Conversely, in Ar + 4%H-2 the fuel self-irradiation field cannot be disregarded since the H2O2 concentrations drop by only three orders of magnitude compared with UO2
• Anomalous electron spin resonance behavior of single-walled carbon nanotubes
  
  • Salvetat J.P.
  • Feher T.
  • L'Huillier C.
  • Beuneu François
  • Forro L.
  Physical Review B: Condensed Matter and Materials Physics (1998-2015), American Physical Society, 2005, 7207, pp.5440. We have studied the electron spin resonance (ESR) of single-walled carbon nanotubes (SWNTs) both in their pristine state and after irradiation with fast electrons in order to detect the signal of conduction electrons. No metallic Pauli contribution was observed in the global spin susceptibility, the ESR signal of the conduction electrons is undetectable because it is broadened by magnetic impurities. We measured a paramagnetic contribution from localized states, with an effective Curie constant decreasing when the temperature increases, following a deactivation law of the type A-B exp(-E-a/k(B)T). This behavior is supposed to be characteristic of semiconducting SWNTs interacting with metallic impurities from the catalyst
• Creation of high energy electronic excitations in inorganic insulators by intense femtosecond laser pulses
  
  • Yatsenko B.N.
  • Bachau H.
  • Belsky A.N.
  • Gaudin J.
  • Geoffroy G.
  • Guizard S.
  • Martin P.
  • Petite G.
  • Philippov A.
  • Vasil'Ev A.N.
  Physica Status Solidi C: Current Topics in Solid State Physics, Wiley, 2005, 2, pp.240. We measured photoemission spectra for a number of insulators (CsI, Diamond, SiO2, CeF3) excited by femtosecond Ti-Sapphire laser pulses at peak intensities, from 0.5 to 6 TW/cm2, which are at least one order of magnitude below the optical breakdown threshold. An intense and pronounced plateau of high energy electrons appears in the photoelectron spectra in this intensity range, which extends up to 30-40 eV at the highest intensities, which we used. The excitation of electrons at high energies is treated in terms of direct interbranch transitions in the conduction band of insulator. These processes are described using calculations based on numerical solution of time dependant Schrödinger equation (TDSE) for Bloch electrons in electric fields
• Optical properties of Si and Ge nanocrystals: Parameter-free calculations
  
  • E. Ramos L.
  • Weissker H.-Ch.
  • Furthmüller J.
  • Bechstedt F.
  physica status solidi (b), Wiley, 2005, 242, pp.3053-3063. An overview is given on the electronic and optical properties of Si and Ge nanocrystals. We model freestanding Si and Ge nanocrystals passivated with H, with up to 363 group-IV atoms and 276 H and oxidized nanocrystals with additional silicon oxide shells, e.g. Si41(O60Si42)(O108Si64)H148. The results discussed are based on parameter-free calculations for relaxed atomic structures. The electronic states and the many-body effects are considered within the density-functional theory and the supercell method. Energy gaps are described within the Kohn–Sham independent-particle picture and within the independentquasiparticle picture, whereas electronic excitations are treated within the delta self-consistent method by pair excitation energies. The projector-augmented wave method allows the calculation of optical matrix elements, oscillator strengths, optical spectra, and radiative lifetimes. We discuss quantum confinement, structural relaxation, oxidation, and the role of defects in oxidized Si NCs.
• New high field state of flux line lattice in CeCoIn5
  
  • Kasahara Y.
  • Watanabe T.
  • Izawa K.
  • Sakakibara T.
  • van Der Beek C.J.
  • Hanaguri T.
  • Nohara M.
  • Takagi H.
  • Shishido H.
  • Settai R.
  • Onuki Y.
  • Matsuda Y.
  Physica C: Superconductivity and its Applications, Elsevier, 2005, 426, pp.36-40. We have measured the ultrasound velocity of quasi-two-dimensional superconductor CeCoIn5 with extremely large Pauli paramagnetic susceptibility. The results indicate that the new high field superconducting phase, which is revealed by the recent heat capacity measurements, is characterized by the unusual softening of flux line lattice. The softening is most likely due to the collapse of the flux line lattice tilt modulus and transition to quasi-two-dimensional vortex state. These results provide a strong evidence that the high field phase is the Fulde–Ferrell–Larkin–Ovchinnikov phase, in which the order parameter is spatially modulated and has planar nodes aligned perpendicularly to the vortices
• Photopolymerization of epoxy coatings containing silica nanoparticles
  
  • Sangermano M.
  • Malucelli G.
  • Amerio E.
  • Priola A.
  • Billi E.
  • Rizza G.
  Progress in Organic Coatings, Elsevier, 2005, 54, pp.134. Silica nanoparticles, were employed to obtain organic-inorganic hybrid coatings via UV curing of an epoxy based system. The influence of the presence Of SiO2 on the rate of polymerization was investigated by real time FT-IR. The silica nanofiller induced both a bulk and a surface modification of UV cured coatings with an increase on T-g, modulus and surface hardness by increasing the amount of silica into the photocurable resin. TEM investigations confirmed that silica filler has a size distribution range between 5 and 50 nm without formation of aggregates. The strong decrease on water uptake in the presence of SiO2 makes these nanocomposites materials particularly interesting for gas-barrier coatings applications
• Analysis of molecular formation in irradiated glasses: a Raman depth profile study
  
  • Ollier N.
  • Boizot B.
  • Reynard B.
  • Ghaleb D.
  • Petite G.
  Journal of Nuclear Materials, Elsevier, 2005, 340, pp.209. Depth profiles experiments have been performed by Raman spectroscopy on three alkali (Na, Li, K) borosilicate glasses irradiated with 1.8 MeV electrons at 1 and 3 GGy. These experiments show that molecular oxigen produced under ß irradiation is concentrated near the glass surface according to a depth depending on the irradiation dose. Moreover, we observed that the polymerisation increase is the same in the entire volume sample. The average Si-O-Si angle decrease under irradiation is also homogenous in the whole irradiated glass volume. From all results, we demonstrate that oxygen migrates up to the glass surface during irradiation without strong irradiation with the glass network. Migration of oxigen and probably alkalis takes through percolation channels with a possible departure of oxygen in some cases
• Investigation of the precipitation kinetics and changes of magnetic anisotropy of iron particles in ion-irradiated silica gel films by means of electron-spin resonance
  
  • Pivin J.C.
  • Esnouf S.
  • Singh F.
  • Avasthi D.K.
  Journal of Applied Physics, American Institute of Physics, 2005, 98, pp.23908. This paper reports the effect of the density of ion-induced electronic excitations on the nucleation of Fe particles in a silicon-based gel and on the magnetic ordering in SiO2:Fe composites with a volume fraction of metal of a few percent derived from the same gel. The nucleation occurs for a critical value of the energy density deposited by ions in electronic excitation. The dependence of the nucleation yield on the ion fluence phi is determined by the product of the electronic energy loss S-e and the number n of ion impacts on a same area a which are necessary for reaching locally this critical energy density. Irradiation-induced changes in the magnetic anisotropy of composite films, previously formed by heat treatment of the same gel, depend more drastically on the order of magnitude of S-e. When the latter is high enough for damaging the matrix, a tilt of the easy magnetization axis is observed
• Thermodynamics of the vortex liquid in heavy-ion-irradiated superconductors
  
  • van Der Beek Cornelis
  • Konczykowski Marcin
  • Fruchter Luc
  • Brusetti René
  • Klein Thierry
  • Marcus Jacques
  • Marcenat C.
  Physical Review B: Condensed Matter and Materials Physics (1998-2015), American Physical Society, 2005, 72 (214504), pp.1-9. It is shown that the large effect of heavy ion irradiation on the thermodynamical properties of the anisotropic superconductor YBa2Cu3O7- extends well into the superconducting fluctuation regime. The presence of the induced amorphous columnar defects shifts the specific-heat maximum at the normal-to-superconducting transition. This effect is similar to that recently put into evidence in cubic KxBa1-xBiO3 x~0.35. In both compounds, vortex pinning manifests itself as a sharp angular dependence of the equilibrium torque. In YBa2Cu3O7-, pinning by the defects appears at the temperature TCp max of the specific-heat maximum, well above the magnetic irreversibility line TirrH. In isotropic KxBa1-xBiO3, the onset of the pinning-related torque anomaly tracks the onset of the specific-heat anomaly and the irreversibility line. In YBa2Cu3O7-, fluctuations of the amplitude of the order parameter and not vortex line wandering are ultimately responsible for the vanishing of pinning. In KxBa1-xBiO3, vortex pinning disappears only at the superconducting-to-normal transition. The results indicate that in both compounds, the pinning energy at the “Bose-glass” transition is large with respect to the total free energy gain in the superconducting state. By implication, the mechanism of this latter transition should be reconsidered.
• Current progress in the magnetism of rare-earth-hydrogen systems
  
  • Vajda P.
  Journal of Alloys and Compounds, Elsevier, 2005, 404-406, pp.131. We are reviewing recent progress obtained in the study of hydrogen interaction with magnetic structures in rare-earth metals, emphasizing the role of the ordering state of the H-sublattice. We shall present in particular: (1) the situation in the solid solutions of the heavy rare earths, alpha*-RHx, and the efforts to relate the special quasi-unidimensional configuration of this phase (charge-density waves) to their modulated magnetism (spin-density waves) via the Fermi surface; (2) an assembly of all magnetic structures determined up to now in the heavy-RE dihydrides, beta-RH(D)(2(+x)), for a tentative comparison of the observed commensurate and/or incommensurate configurations; special mention will be made of the remarkably stable short-range ordered (SRO) magnetism always present in these systems; (3) the need for further (thorough) neutron scattering work on the magnetism in the insulating R-trihydrides, gamma-RH(D)(3(-x)), in order to specify its mechanism in the absence of RKKY exchange interaction
• Comment on “Quantum Confinement and Electronic Properties of Silicon Nanowires”
  
  • Bruneval Fabien
  • Botti Silvana
  • Reining Lucia
  Physical Review Letters, American Physical Society, 2005, 94, pp.219701. A Comment on the Letter by Xinyuan Zhao et al., Phys. Rev. Lett. 92, 236805 (2004). The authors of the Letter offer a Reply. (10.1103/PhysRevLett.94.219701)
  DOI : 10.1103/PhysRevLett.94.219701
• Ferromagnetic Domain Structure of La0.78Ca0.22MnO3 Single Crystals
  
  • Jung Grzegorz
  • Markovich Vladimir
  • van Der Beek Cornelis Jacominus
  • Mogilyansky Dmitrii
  • Mukovskii Yakov M.
  Physical Review B: Condensed Matter and Materials Physics (1998-2015), American Physical Society, 2005, 72, pp.134412. The magneto-optical technique has been employed to observe spontaneous ferromagnetic domain structures in La0.78Ca0.22MnO3 single crystals. The magnetic domain topology was found to be correlated with the intrinsic twin structure of the investigated crystals. With decreasing temperature the regular network of ferromagnetic domains undergoes significant changes resulting in apparent rotation of the domain walls in the temperature range of 70-150 K. The apparent rotation of the domain walls can be understood in terms of the Jahn-Teller deformation of the orthorhombic unit cell, accompanied by additional twinning.
• Concave and Convex photonic Barriers in Gradient Optics
  
  • Shvartsburg Alexandr B.
  • Petite Guillaume
  The European Physical Journal D : Atomic, molecular, optical and plasma physics, EDP Sciences, 2005, 36, pp.111. Propagation and tunneling of light through photonic barriers formed by thin dielectric films with continuous curvilinear distributions of dielectric susceptibility across the film, are considered. Giant heterogeneity-induced dispersion of these films, both convex and concave, and its influence on their reflectivity and transmittivity are visualized by means of exact analytical solutions of Maxwell equations. Depending on the cut-off frequency of the film, governed by the spatial profile of its refractive index, propagation or tunneling of light through such barriers are examined. Subject to the shape of refractive index profile the group velocities of EM waves in these films are shown to be either increased or deccreased as compared with the homogeneous layers; however, these velocities for both propagation and tunneling regimes remain subluminal. The decisive influence of gradient and curvature of photonic barriers on the efficiency of tunneling is examined by means of generalized Fresnel formulae. Saturation of the phase of the wave tunneling through a stack of such films (Hartman effect), is demonstrated. The evanescent modes in lossy barriers and violation of Hartman effect in this case is discussed.
• Anomalous electron spin resonance behavior of single-walled carbon nanotubes
  
  • Beuneu Francois
  • Salvetat J.-P.
  • Fehér T.
  • L'Huillier C.
  • Forró L.
  Physical Review B: Condensed Matter and Materials Physics (1998-2015), American Physical Society, 2005, 72, pp.075440. We have studied the electron spin resonance ESR of single-walled carbon nanotubes SWNTs both in their pristine state and after irradiation with fast electrons in order to detect the signal of conduction electrons. No metallic Pauli contribution was observed in the global spin susceptibility, the ESR signal of the conduction electrons is undetectable because it is broadened by magnetic impurities. We measured a paramagnetic contribution from localized states, with an effective Curie constant decreasing when the temperature increases, following a deactivation law of the type A-B exp-Ea /kBT. This behavior is supposed to be characteristic of semiconducting SWNTs interacting with metallic impurities from the catalyst. (10.1103/PhysRevB.72.075440)
  DOI : 10.1103/PhysRevB.72.075440
• TDDFT from molecules to solids: The role of long-range interactions
  
  • Sottile F.
  • Bruneval F.
  • G. Marinopoulos A.
  • K. Dash L.
  • Botti Silvana
  • Olevano Valério
  • Vast N.
  • Rubio A.
  • Reining L.
  International Journal of Quantum Chemistry, Wiley, 2005, 102, pp.684. Classical Hartree effects contribute substantially to the success of time-dependent density functional theory, especially in finite systems. Moreover, exchange-correlation contributions have an asymptotic Coulomb tail similar to the Hartree term, and turn out to be crucial in describing response properties of solids. In this work, we analyze in detail the role of the long-range part of the Coulomb potential in the dielectric response of finite and infinite systems, and elucidate its importance in distinguishing between optical and electron energy loss spectra (in the long wavelength limit q 0). We illustrate numerically and analytically how the imaginary part of the dielectric function and the loss function coincide for finite systems, and how they start to show differences as the distance between objects in an infinite array is decreased (which simulates the formation of a solid). We discuss calculations for the model case of a set of interacting and noninteracting beryllium atoms, as well as for various realistic systems, ranging from molecules to solids, and for complex systems, such as superlattices, nanotubes, nanowires, and nanoclusters. (10.1002/qua.20486)
  DOI : 10.1002/qua.20486