Publications

2009

• Transport properties of vortex matter governed by the edge inductance in superconducting Bi2Sr2CaCu2O8 crystals
  
  • Beidenkopf Haim
  • Myasoedov Yuri
  • Zeldov Eli
  • Brandt Ernst Helmut
  • Mikitik Grigorii P
  • Tamegai Tsuyoshi
  • Sasagawa Takao
  • van Der Beek Cornelis Jacominus
  Physical Review B: Condensed Matter and Materials Physics (1998-2015), American Physical Society, 2009, 80, pp.224526. We study the distribution of transport current across superconducting Bi2Sr2CaCu2O8 crystals and the vortex flow through the sample edges. We show that the Tx transition is of electrodynamic rather than thermodynamic nature, below which vortex dynamics is governed by the edge inductance instead of the resistance. This allows measurement of the resistance down to 2 orders of magnitude below the transport noise. By irradiating the current contacts the resistive step at vortex melting is shown to be due to loss of c-axis correlations rather than breakdown of quasilong-range order within the a-b planes. (10.1103/PhysRevB.80.224526)
  DOI : 10.1103/PhysRevB.80.224526
• Field-periodic magnetoresistance oscillations in thin graphite single crystals with columnar defects
  
  • Latyshev Yuri I.
  • Latyshev A. Yu
  • Orlov Andrei P.
  • Chekin A. A.
  • Bykov V. A.
  • Monceau Pierre
  • van Der Beek Cornelis Jacominus
  • Konczykowski Marcin
  • Monnet Isabelle
  JETP Letters, Springer Verlag, 2009, 90 (6), pp.480-484. (10.1134/S0021364009180167)
  DOI : 10.1134/S0021364009180167
• On the origins of the Finnis-Sinclair potentials
  
  • Hardouin Duparc Olivier
  Philosophical Magazine, Taylor & Francis, 2009, 89 (34-36), pp.3117-3131. I trace back the origins of the famous Finnis-Sinclair potentials. These potentials mimic the results of tight binding theory through their use of the square root embedding function. From the tentative beginnings of tight binding in the 1930s up to 1984 or so, some of the famous names involved are Bloch, Seitz, Montroll, Friedel, Cyrot-Lackmann, Ducastelle, to name just a few. The application of the method of moments to the description of densities of states and its connexion to the physics of closed paths linking nearest neighbours interacting atoms helped to formalize Friedel's rectangular band model for the d electrons in transition metals. Extension from perfectly periodic structures to defective ones could not be but a slow process due to the change of paradigm for solid state scientists and to the necessary caution to be paid to self-consistency. The British scientists school also contributed significantly in the 80s. Computer progress and pragmatism helped to go from mainly analytical developments to numerical experiments (another change of paradigm). I also digress on various not so well known historical points of interest to this story. (10.1080/14786430903292423)
  DOI : 10.1080/14786430903292423
• Direct dynamical coupling of spin modes and singlet Josephson supercurrent in ferromagnetic Josephson junctions
  
  • Petkovic Ivana
  • Aprili M.
  • Barnes S.E.
  • Beuneu Francois
  • Maekawa S.
  Physical Review B: Condensed Matter and Materials Physics (1998-2015), American Physical Society, 2009, 80, pp.220502. Via a direct coupling between the order parameter and the singlet Josephson supercurrent we detect spin-wave resonances and their dispersion in ferromagnetic Josephson junctions in which the usual insulating or metallic barrier is replaced with a weak ferromagnet. The coupling arises within the Fraunhofer interferential description of the Josephson effect because the magnetic layer acts as a time-dependent phase plate. A spin-wave resonance at a frequency omega(s) implies a dissipation that is reflected as a depression in the current-voltage curve of the Josephson junction when h omega(s)=2eV. We have thereby performed a resonance experiment on only 10(7) Ni atoms. (10.1103/PhysRevB.80.220502)
  DOI : 10.1103/PhysRevB.80.220502
• Quantum thermal bath for molecular dynamics simulation
  
  • Dammak Hichem
  • Chalopin Yann
  • Laroche Marine
  • Hayoun Marc
  • Greffet Jean-Jacques
  Physical Review Letters, American Physical Society, 2009, 103 (19), pp.190601. Molecular dynamics (MD) is a numerical simulation technique based on classical mechanics. It has been taken for granted that its use is limited to a large temperature regime where classical statistics is valid. To overcome this limitation, the authors introduce in a universal way a quantum thermal bath that accounts for quantum statistics while using standard MD. The efficiency of the new technique is illustrated by reproducing several experimental data at low temperatures in a regime where quantum statistical effects cannot be neglected. (10.1103/PhysRevLett.103.190601)
  DOI : 10.1103/PhysRevLett.103.190601
• Microwave absorption in YBa[2]Cu[3]O[7-delta]-manganite superlattices
  
  • Gierlowski Piotr
  • Werner-Malento Krzysztof
  • Przyslupski Piotr
  • van Der Beek Cornelis Jacominus
  Applied Physics Letters, American Institute of Physics, 2009, 95 (17), pp.172511-1. We report on results of direct microwave absorption measurements of Re1−x Bx MnO3 /YBa2 Cu3 O7−δ half metal/d-wave superconductor superlattices (where Re - La and Pr) and (B - Sr and Ca) for microwave frequencies in the range from 9 to 20 GHz. The measurements of the entire heterostructure were performed mostly at temperatures below the superconducting transition. The obtained results strongly depend on the microwave frequency and can be qualitatively described within the theoretical model of high-frequency properties of Josephson junctions with a ferromagnetic barrier proposed by S. Takahashi, S. Hikino, M. Mori, J. Martinek, and S. Maekawa, Phys. Rev. Lett. 99, 057003 (2007). (10.1063/1.3255012)
  DOI : 10.1063/1.3255012
• Thermodynamique des vortex dans les supraconducteurs désordonnés
  
  • van Der Beek Cornelis Jacominus
  , 2009. L'avènement des supraconducteurs à haute température critique (SHTc) a non seulement bouleversé les notions fondamentales de la physique des solides, il a aussi provoqué une révolution dans la compréhension du comportement des lignes de flux magnétiques quantifiés qui traversent le matériau supraconducteur lorsqu'il est exposé à un champ magnétique. Grâce à la coincidence des valeurs extrèmes des paramètres caractérisant la supraconductivité dans les SHTc, les propriétés physiques des vortex, leur dynamique, et leur diagramme de phases dans le plan (B,T) ont pu être étudiés dans un détail jusque-là inaccessible. Il a ainsi été établi que la véritable transition de la phase supraconductrice vers la phase normale n'a pas lieu au deuxième champ critique Bc2, mais à la transition de fusion de l'ensemble des lignes de flux. Dans des matériaux supraconducteurs désordonnés, il apparaît une nouvelle phénoménologie, liée à l'ancrage des lignes de flux sur les défauts du matériau. De nouvelles phases thermodynamiques de vortex ancrés ont été postulés, et, dans certains cas, trouvées. Le but de ce document est de porter un regard critique sur le mécanisme menant à la transition de fusion de l'ensemble des vortex dans les SHTc, ainsi que sur le rôle du désordre cristallin dans la physique des lignes de flux. L'approche première est de, avant tout, caractériser au mieux les matériaux avec lesquels on travaillera par la suite. Cette caractérisation inclut non seulement la mesure des principaux paramètres de la supraconductivité: température critique, longueur de pénétration, champs critiques; mais aussi le contrôle de la pureté des matériaux et du désordre cristallin éventuel. Dans cette optique, le travail s'inscrit dans la mission du Laboratoire des Solides Irradiés, qui est d'accéder à la physique des matériaux en contrôlant le désordre par irradiation. On essaiera ensuite d'attaquer la transition de fusion par l'emploi d'une méthode originale, utilisable dans les SHTc lamellaires comme le Bi2Sr2CaCu2O8 : la Résonance de Plasma Josephson. Cette technique permettra d'évaluer les excursions thermiques moyennes des lignes de flux au voisinage de la transition, dans des cristaux bruts de croissance et irradiés. Le rôle du désordre cristallin est étudié également par une approche novatrice: c'est l'étude de la modification des propriétés thermodynamiques par le désordre, plutôt que les propriétés de transport. Enfin, on conclut sur comment ces approches peuvent nous aider à comprendre le diagramme de phases des lignes de flux dans des supraconducteurs désordonnés de manière contrôlée.
• Étude de l'environnement et des propriétés optiques des ions Ti3+ formés sous irradiation ionisante dans les verres d'oxyde
  
  • Lombard Pierre
  , 2009. Nous avons étudié par spectroscopie de Résonance Paramagnétique Électronique (RPE), par simulation de spectre RPE, par spectroscopie Raman et par photoluminescence les ions Ti3+ formés par irradiation aux β de 3,37 x 10^5 à 1,68 x 10^9 Gy dans les verres SiO2 - Na2O - TiO2 et SiO2 - Al2O3 - B2O3 - Na2O - TiO2. Nous montrons que ces ions existent dans les verres silicatés dans trois sites différents correspondant à trois environnements différents : [VI]Ti3+, [V]Ti3+ sous forme de pyramide à base carrée et peut être sous forme de bi-pyramide. Il existe de même trois sites des ions Ti3+ dans les verres alumino-borosilicatés et le site des ions [VI]Ti3+ est commun aux deux classes de verres. L'étude de l'évolution des proportions d'ions Ti3+ dans chacun des sites ainsi que l'étude des paramètres RPE des sites montre que leur existence est déterminée par la dose intégrée et la valeur du rapport [Na]/[Ti] que nous redéfinissons dans le cas des verres alumino-borosilicatés. Enfin, sous une excitation à 266 nm nous observons à température ambiante une bande d'émission à 500 nm attribuée aux ions Ti4+. Sous une excitation à 532 nm, nous observons une bande d'émission à 590 nm avec des temps de vie courts d'une centaine de ns que nous attribuons soit aux ions Ti3+ soit à des défauts formés près des ions Ti4+. Dans l'ensemble, cette étude montre donc qu'il est possible de contrôler par la chimie et la dose intégrée l'environnement des ions Ti3+ et donc les propriétés d'émission de cet ion dans un verre.
• Binary potassium-silicate glass irradiated with electrons
  
  • Gedeon O.
  • Jurek K.
  • Drbohlav I.
  • Ollier Nadège
  Nuclear Instruments and Methods in Physics Research Section B: Beam Interactions with Materials and Atoms, Elsevier, 2009, 267, pp.3461-3465. (10.1016/j.nimb.2009.07.022)
  DOI : 10.1016/j.nimb.2009.07.022
• ÉTUDE THÉORIQUE DES RÉACTIONS D'OLIGOMÉRISATION DES OLÉFINES CATALYSÉES PAR DES COMPLEXES DU FER
  
  • Raucoules R.
  , 2009. Les catalyseurs bis(imino)pyridine au fer sont hautement actifs en oligo- ou polymérisation des oléfines. L'IFP souhaite étudier ces catalyseurs pour transformer l'éthylène en oléfines linéaires de tailles maîtrisées. Cependant, l'étape d'activation du précurseur (usuellement avec le cocatalyseur MAO) génère une espèce activée dont la nature reste à ce jour inconnue. Nos calculs DFT montrent que l'espèce activée la plus réactive est dans un état d'oxydation +III et de spin quadruplet. Le fait que nos calculs, en combinaison avec un modèle microcinétique, décrivent précisément les résultats expérimentaux d'oligomérisation du butène-1, c'est-à-dire la formation majoritaire d'octènes linéaires, fournit un support additionnel à la pertinence de l'espèce activée retenue. Par ailleurs, l'utilisation de ce modèle moléculaire a permis d'établir une puissante corrélation entre le coefficient Schulz-Flory, qui informe du degré d'oligo- ou de polymérisation expérimental d'un catalyseur, et la différence des enthalpies libres d'activation d'une réaction d'insertion et de terminaison particulières. Cette relation nous a permis d'étudier et de mieux comprendre le comportement des catalyseurs bis(arylimino)pyridine au fer vis-à- vis des changements de substituants. En outre, son fort potentiel universel est montré grâce à l'extension de son domaine d'application vers d'autres catalyseurs (autres ligands, autres métaux). Enfin, les liaisons agostiques dans les complexes bis(arylimino)pyridine ont été étudiées par des calculs QTAIM parce qu'elles sont souvent un prélude aux réactions de terminaison dans les cycles catalytiques.
• On the structure-properties relationship of the AMV anion exchange membrane
  
  • Xt (le Xuan Tuan) Le
  • Th (bui Thi Hao) Bui
  • Viel Pascal
  • T (berthelot Thomas) Berthelot
  • Palacin Serge
  Journal of Membrane Science, Elsevier, 2009, 340 (1-2), pp.133-140. Important parameters such as ion exchange capacity, conductivity, permselectivity, quantity of sorbed electrolyte and water uptake of the Selemion AMV anion exchange membrane conditioned in KCl and NaCl solutions were determined in order to assess the applicability of the two-phase model of structure microheterogeneity to this case. In general, a good consistency between the experimental results and the theoretical approach was obtained. Electrical conductivity measurements allowed evaluating the volume fractions of two distinct internal phases inside the membrane. Aside from the chronopotentiometric behaviour of the AMV membrane, SEM and XPS techniques contributed to provide a better description of the overall membrane homogeneity. Influence of co-ions in relation with water uptakes on the conductivity and permselectivity of the studied membrane has been shown. An existence of partition equilibrium between the electrolytes sorbed in the membrane and the external solution confirmed in this work should be introduced within the microheterogeneous model
• Disorder and flux pinning in superconducting pnictide single crystals
  
  • van Der Beek Cornelis Jacominus
  • Rizza Giancarlo
  • Konczykowski Marcin
  • Fertey Pierre
  • Monnet Isabelle
  • Okazaki Ryuji
  • Kato Terukazu
  • Hashimoto Kenishiro
  • Shimozawa M.
  • Shishido Hiroaki
  • Yamashita Minoru
  • Ishikado Motoyuki
  • Kito Hijiri
  • Iyo Akira
  • Eisaki Hiroshi
  • Shamoto Shin-Ichi
  • Shibauchi Takasada
  • Matsuda Yuji
  , 2009. Crystalline disorder in the pnictide superconductor PrFeAsO1−y is studied using magneto-optical visualisation of flux penetration, Transmission Electron Microscopy, and X-ray diffraction using synchrotron radiation. Critical-state like flux distributions and the magnitude and temperature dependence of the critical current demonstrate bulk vortex pinning by oxygen vacancies at all temperatures. (10.1016/j.physc.2009.11.089)
  DOI : 10.1016/j.physc.2009.11.089
• Atomistic segregation analysis in an asymmetrical grain boundary for Ni(Ag)
  
  • Djerouni N. E. H.
  • Khalfallah O.
  • Hardouin Duparc Olivier
  Proceedings of the JMSM 2008 Conference, 2009, 2, pp.1359-1368. Intergranular segregation is studied for the first time in an asymmetrical grain boundary at the atomistic level. The grain boundary (GB) is the asymmetrical tilt (331)//(11-1) < 110 > experimentally observed by high resolution transmission electron microscopy (HRTEM) in nickel bicrystal. The metallic alloy chosen for the study is nickel(silver) in the limit of infinity diluted solution. The interactions are modelled with n-body, Finnis-Sinclair like, potentials. The atomic sites are characterized by their exact Voronoi volumes and by the stress density tensors locally exerted. In these respects, the asymmetrical near Sigma=11 (331)//(11-1) GB presents a larger diversity of sites than the symmetrical GBs previously studied. The segregation energies are computed and analyzed versus the two 'driving forces', the elastic size effect and the excess cohesion energy effect, which play a role in metallic intergranular segregation in the one atom segregation limit. The elastic size effect calculated by the method of virtual impurity represents the main segregation driving force in most cases of the considered bimetallic alloy. This generalizes to an asymmetrical GB results previously obtained on symmetrical GBs. (C) 2009 Elsevier B.V. All rights reserved
• Hybrid Organic/Inorganic UV-Cured Acrylic Films with Hydrophobic Surface Properties
  
  • M (sangermano Marco) Sangermano
  • R (bongiovanni Roberta) Bongiovanni
  • M (longhinmarco) Longhin
  • G (rizza Giancarlo) Rizza
  • Cm (kausch Charles M.) Kausch
  • y (kim Yongsin) Kim
  • Rr (thomas Richard R.) Thomas
  Macromolecular Materials and Engineering, Wiley-VCH Verlag, 2009, 294 (8), pp.525-531. Hybrid organic/inorganic acrylic nanostructured films were prepared by a UV/thermal dual-curing process. The role of a fluorinated hydroxyl acrylate monomer (AF) as coupling agent was investigated. Increased T-g values and modulus of the dual-cured films were achieved by increasing the TEOS inorganic precursor. The coupling agent deeply modified the surface properties of the cured films: the formation of hybrid films characterized by high hydrophobicity together with an increase on surface hardness was achieved. TEM analysis clearly evidenced the reducing of the nanosize dimensions of the inorganic silica domains by increasing the coupling agent content in the photocurable formulation
• Identification of potential cellular targets of aloisine A by affinity chromatography.
  
  • Corbel Caroline
  • Haddoub Rose
  • Guiffant Damien
  • Lozach Olivier
  • Gueyrard David
  • Lemoine Jérôme
  • Ratin Morgane
  • Meijer Laurent
  • Bach Stéphane
  • Goekjian Peter
  Bioorganic and Medicinal Chemistry, Elsevier, 2009, 17 (15), pp.5572-82. Affinity chromatography was used to identify potential cellular targets of aloisine A (7-n-butyl-6-(4'-hydroxyphenyl)-5H-pyrrolo[2,3b]pyrazine), a potent inhibitor of cyclin-dependent kinases. This technique is based on the immobilization of the drug on a solid matrix, followed by identification of specifically bound proteins. To this end, both aloisine A and the protein-kinase inactive control N-methyl aloisine, bearing extended linker chains have been synthesized. We present the preparation of such analogues having the triethylene glycol chain at different positions of the molecule, as well as their immobilization on an agarose-based matrix. Affinity chromatography of various biological extracts on the aloisine matrices allowed the identification of both protein kinases and non-kinase proteins as potential cellular targets of aloisine. (10.1016/j.bmc.2009.06.024)
  DOI : 10.1016/j.bmc.2009.06.024
• Competing mechanisms in the atomic diffusion of a MgO admolecule on the MgO(001) surface
  
  • Geneste Grégory
  • Hayoun Marc
  • Finocchi Fabio
  • Morillo Joseph
  Journal of Physics: Condensed Matter, IOP Publishing [1989-....], 2009, 21 (31), pp.315004. The diffusion mechanism of a MgO admolecule on a flat MgO(001) surface has been investigated by equilibrium molecular dynamics simulation. Care has been taken in the choice of the phenomenological interionic potential used. Four distinct mechanisms have been found and the corresponding dynamical barriers determined at high temperature. Some static barriers have also been computed for comparison and all intermediate configurations have been obtained with the same phenomenological potential and also by the DFT-GGA approach. The hopping mechanisms involving the Mg adatom, although dominant, must be combined with the infrequent mechanisms involving displacements of O adatoms in order to provide the mass transport on the surface, which is crucial for crystal growth both in the nucleation and step-flow regimes (10.1088/0953-8984/21/31/315004)
  DOI : 10.1088/0953-8984/21/31/315004
• First reductive dimerization of a polycyclic azine
  
  • Berthet Jean Claude
  • Thuéry Pierre
  • Baudin Cécile
  • Boizot Bruno
  • Ephritikhine Michel
  Dalton Transactions, Royal Society of Chemistry, 2009, 37, pp.7613. The tptz molecule is reduced by potassium into its anion-radical in the compound K(tptz)2 (1), whereas it is reductively coupled by SmI2 and UI3(py)4 into the bis-triazinide ligand in the dinuclear complexes [Sm2(tptz– tptz)(DMF)8][I]4·3.5DMF (2·3.5DMF) and U2I6(tptz– tptz)(MeCN)2·2MeCN (3·2MeCN) where each metal ion occupies a pentadentate N5 cavity of the [tptz–tptz]2– ligand. (10.1039/b909547k)
  DOI : 10.1039/b909547k
• Oxidation state variation under beta-irradiation in an iron-bearing soda lime glass system
  
  • Rossano Stéphanie
  • Jean-Soro Liliane
  • Boizot Bruno
  • Farges Francois
  • van Hullebusch Eric D.
  • Labanowski J.
  • Gouzin L.
  • Combes R.
  • Linares Jorge
  • Swarbrick J.C.
  • Harfouche M.
  , 2009, 190, pp.012194. The effect of ionizing radiation on glasses in the system SiO2-CaO-Na2O-Fe2O3 is investigated as a function of iron concentration or / and irradiation dose by a pre-edge analysis at the iron K-edge. While reduction phenomenon is clearly observed for large irradiation doses (5 C), the effect of irradiation for intermediate doses is more challenging to interpret. Comparison between X-ray absorption measurements, colorimetry results and Electron Paramagnetic Resonance measurements suggest that iron environment may be modified without the ions being reduced. (10.1088/1742-6596/190/1/012194)
  DOI : 10.1088/1742-6596/190/1/012194
• Conductance of disordered semiconducting nanowires and carbon nanotubes: a chain of quantum dots
  
  • Dayen J.-F.
  • Wade T.L.
  • Rizza G.
  • Golubev D.S.
  • Cojocaru C.-S.
  • Pribat D.
  • Jehl X.
  • Sanquer M.
  • Wegrowe J.-E.
  European Physical Journal: Applied Physics, EDP Sciences, 2009, 48 (1), pp.1-14. A comparative study of the low temperature conductivity of an ensemble of multiwall carbon nanotubes and semiconductor nanowires is presented. The quasi one-dimensional samples are made in nanoporous templates by electrodeposition and CVD growth. Three different structures are studied in parallel: multiwall carbon nanotubes, tellurium nanowires, and silicon nanowires. It is shown that the Coulomb blockade regime dominates the electronic transport below 50 K, together with weak and strong localization effects. In the Coulomb blockade regime, a scaling law of the conductance measured as a function of the temperature and the voltage is systematically observed. This allows a single scaling parameter to be defined. This parameter accounts for the specific realization of the “disorder”, and plays the role of a fingerprint for each sample. Correlations between and the conductance measured as a function of temperature and voltage, as a function of the perpendicular magnetic field, and as a function of the temperature and voltage in the localized regime below 1 K have been performed. Three universal laws are reported. They relate the coefficient (1) to the normalized Coulomb blockade conductance , (2) to the phase coherence length , and (3) to the activation energy . These observations suggest a description of the wires and tubes in terms of a chain of quantum dots; the wires and tubes break into a series of islands. The quantum dots are defined by conducting islands with a typical length on the order of the phase coherence length separated by poorly conducting regions (low density of carriers or potential barriers due to defects). A corresponding model is developed in order to put the three universal laws in a common frame. (10.1051/epjap/2009132)
  DOI : 10.1051/epjap/2009132
• Strongly dissimilar vortex-liquid regimes in single-crystalline NdFeAs(O,F) and (Ba,K)Fe2As2: A comparative study
  
  • Kacmarcik Jozef
  • Marcenat C.
  • Klein Thierry
  • Pribulova Zuzana
  • van Der Beek Cornelis Jacominus
  • Konczykowski Marcin
  • Bud'Ko Serguey
  • Tillman Matthew
  • Ni Ni
  • Canfield Paul C.
  Physical Review B: Condensed Matter and Materials Physics (1998-2015), American Physical Society, 2009, 80 (1), pp.014515. The extent of the vortex-liquid state in underdoped single crystals of the oxypnictide superconductors NdFeAs(O,F) and (Ba,K)Fe2As2 is investigated using specific heat (C-p) and Hall-probe magnetization experiments. In both materials, the vortex liquid lies entirely in the regime where the three-dimensional lowest Landau-level (3D-LLL) approximation is valid and both systems present a very small shift in the specific heat anomaly with increasing field. The irreversibility line, defined as the onset of diamagnetic response, is very rapidly shifted toward lower temperatures in NdFeAs(O,F) but remains close to the C-p anomaly in (Ba,K)Fe2As2. These measurements strongly suggest that a vortex-liquid phase occupies a large portion of the mixed-state phase diagram of NdFeAs(O,F) but not in (Ba,K)Fe2As2. This difference can be attributed to different Ginzburg numbers Gi, the latter being about 100 times larger in NdFeAs(O,F) than in (Ba,K)Fe2As2. The angular dependence of the upper critical field, derived from 3D-LLL scaling of the irreversibility lines, presents deviations from the standard 3D effective-mass model in both materials with an anisotropy being about three times smaller in (Ba,K)Fe2As2 (gamma similar to 2.5) than in Nd(F,O)FeAs (gamma similar to 7.5). (10.1103/PhysRevB.80.014515)
  DOI : 10.1103/PhysRevB.80.014515
• Enhancement of the field of first flux penetration due to Andreev bound states in Bi_2Sr_2CaCu_2O_8+delta
  
  • van Der Beek Cornelis
  • Böhmer Anna Elisabeth
  • Konczykowski Marcin
  , 2009. First flux penetration into single crystalline Bi_2Sr_2CaCu_2O_8+delta is investigated using magneto-optical imaging and Hall probe array magnetometry. Below 50 K, a slight enhancement of the field of first flux penetration, H_p, is found when the edge normals are oriented at 45° with respect to the principal (ab) crystal axes, rather than parallel to them. We discuss this effect in terms of a role of Andreev bound states [C. Iniotakis, T. Dahm, and N. Schopohl, Phys. Rev. Lett. 100, 037002 (2008).]
• Joule heating and high frequency nonlinear effects in the surface impedance of high Tc superconductors
  
  • Kermorvant Julien
  • van Der Beek Cornelis Jacominus
  • Mage Jean-Claude
  • Marcilhac Bruno
  • Lemaître Yves
  • Briatico Javier
  • Bernard Rozenn
  • Villegas Javier
  Journal of Applied Physics, American Institute of Physics, 2009, 106, pp.023912. Using the dielectric resonator method, we have investigated nonlinearities in the surface impedance Zs = Rs + jXs of YBa2Cu3O7 thin films at 10 GHz as function of the incident microwave power level and temperature. The use of a rutile dielectric resonator allows us to measure the precise temperature of the films. We conclusively show that the usually observed increase of the surface resistance of YBa2Cu3O7 thin film as function of microwave power is due to local heating. (10.1063/1.3079520)
  DOI : 10.1063/1.3079520
• Microscopic Magnetic Study of Ordinary Chondrite Using Magneto-Optical Imaging
  
  • Uehara M.
  • Gattacecca J.
  • van Der Beek Cornelis Jacominus
  , 2009, 44, pp.A208-A208. We present new advances in the microscopic magneto-optical imaging (MOI) technique applied to rock magnetism. This technique uses the Faraday effect of a thick MO active film. The propagation of linearly polarized light parallel to the direction of magnetization of the film induces a rotation of the polarization direction of the light (Faraday rotation). For small magnetic components BZ oriented perpendicularly to the film, the Faraday angle of rotation of the polarization of perpendicular incident light is given by aF = VBZd, where V is the Verdet constant of the MO material, and d is the thickness of MO active film. Therefore, when the MO film is placed on top of a sample, the MOI technique images the perpendicular component of the magnetic field at the specimen surface. The flux density Bz is observed through the analyzer of a polarized light microscope. The MO film, or indicator, used in the present study is a bi-doped Yttrium-Iron-Garnet film of thickness 5 mm, deposited on Gadolinium-Gallium Garnet substrate (thickness 500 mm), and covered by a reflecting Al mirror (100 nm). This configuration enables us to observe magnetic fields at the surface of polished samples, such as rocks,. In this geometry, light passes through the MO active film twice, and thus the angle of rotation and the sensitivity is doubled (aF = 2VBZd). The contrast of the MO images depends on the relative angular orientation position of polarizer and analyzer. On typically obtains a contrast between bright and dark regions corresponding to field parallel (antiparallel) to the sample normal. Subtraction of images obtained at two different analyzer angles ( polarization modulation technique) increases the contrast in image of samples carrying a weak magnetization, such as natural remanent magnetization (NRM). We have obtained MO images with high spatial resolution of about 10 µm, owing to the thin MO active layer and the small sample-to-layer distance. Besides its good spatial resolution (with respect to magnetic scanning techniques), one of the main advantages is the direct comparison of the magnetic image and the reflected light image taken with the same microscope. For instance, we have successfully imaged internal structures in metallic grains in meteorites carrying SIRM. Even in the NRM state, the MOI technique combined with polarization modulation can reveal small dipole-like features within a metal grain in meteorites. Thus, the MOI technique can image surface magnetic field with 10 µm spatial resolution and appears as a very powerful tool to identify the components responsible for remanence in rock samples
• Some ab initio studies of the physical properties of materials
  
  • Vast Nathalie
  , 2009. My activities are in fundamental research in the group of theory of the Laboratoire des Solides Irradiés. It includes the study of the physical properties of some of those materials which are of interest to the CEA, to nuclear research and to nanoelectronics. The objective is to achieve a parameter-free description of processes which control electronic excitations or electronic relaxations. This covers : - The study of the ground state of materials; - The investigation of the properties of the excited state, from the viewpoint of the spectroscopy of valence electrons; - The lattice dynamics, its coupling with phonons, and the effect of electron-phonon coupling on electronic transport and electronic relaxation. These studies involves high performance computing and require computer time from big facilities like the GENCI in France. In the manuscript, I recall first how the inverse dielectric function is calculated within time dependent, density functional theory, and the link with the measurement of the electronic loss function. Theoretical results are presented for titania TiO$_2$ and zirconia ZrO$_2$ which are uncorrelated oxides. Then main theoretical results on optical absorption of cuprous oxide Cu$_2$O and on zirconia ZrO$_2$ are presented. A new interpretation on the kernel which allows to model excitonic effects in time dependent density functional theory is presented. Finally, recent calculations on boron carbides, and in particular B$_4$C are reviewed.
• Heterogeneous vortex dynamics in high temperature superconductors
  
  • Yang Feng
  , 2009. In high temperature superconductors with strong pinning, the change in shear properties of the vortex system is a plausible mechanism for the vanishing of the linear electrical resistance at the transition from vortex liquid to vortex solid. The divergence of the shear viscosity of the vortex liquid upon cooling is, in this respect, an ominent sign of a phase transition to an ensemble of localized vortices. By introducing a channel-confined structure on macroscopic defect-free $Bi_{2}Sr_{2}CaCu_{2}O_{8}$ single crystals using heavy ion irradiation, we have succeeded in probing the shear viscosity of the vortex liquid directly. Magneto-optical imaging shows that 20 $\mu$m wide pin-free channels separated by 20 $\mu$m wide strongly pinning walls were made successfully. The vortex liquid shear viscosity was then obtained from transport measurements. Contrary to previous studies, the present work focuses on very low magnetic fields, of the order of hundreds of Gauss. The vortex liquid shear viscosity, even in low fields, can be equally well fitted by the Nelson-Halperin theory for the dislocation density in a two-dimensional vortex fluid as by the power laws derived in the framework of vortex glass models. This result shows that the vortex ensemble in the confined medium behaves as a system of rectilinear lines, with edge dislocations threading the system from end to end. The progressive jamming of the vortex ensemble upon cooling mimics a vortex liquid to vortex glass transition. This finds an analogy with recently reported shear-induced solid-to-fluid transitions in soft glassy materials.