Publications

2007

• High-field superconducting transition of CeCoIn5 studied by local magnetic induction measurements
  
  • Okazaki Ryuji
  • Shishido Hiroaki
  • Shibauchi Takasada
  • Konczykowski Marcin
  • Buzdin Alexandre I.
  • Matsuda Yuji
  Physical Review B: Condensed Matter and Materials Physics (1998-2015), American Physical Society, 2007, 76 (22), pp.224529 (1-5). To investigate the unusual normal-superconducting phase transition near the upper critical fields at low temperatures of the quasi-two-dimensional heavy fermion compound CeCoIn5, local magnetic induction measurements have been performed by using a micro Hall probe for both H||c and H||a. The local magnetic induction as a function of temperature displays a discontinuous jump at the superconducting phase boundary below the critical temperature T0 approximate to 0.8 K for both field directions, indicating a change from the second- to first-order transition and confirming previously reported bulk measurements on CeCoIn5. The magnetic induction data display an unexpected undershoot behavior just below the jump down, which has never been reported in the bulk measurements. This undershoot is observed at the phase boundary between the normal state and the high-field superconducting phase, which has been attributed to the spatially inhomogeneous Fulde-Ferrell-Larkin-Ovchinnikov state. Possible origins of this unusual undershoot behavior are discussed. (10.1103/PhysRevB.76.224529)
  DOI : 10.1103/PhysRevB.76.224529
• Positronium reemission yield from mesostructured silica films
  
  • Laszlo Liszkay
  • Corbel Catherine
  • Perez Patrice
  • Desgardin Pierre
  • Barthe M.-F.
  • Ohdaira Toshiyuki
  • Suzuki Ryoichi
  • Crivelli Paolo
  • Gendotti Ulisse
  • Rubbia André
  • Etienne Matieu
  • Walcarius Alain
  , 2007. The reemission yield of ortho-positronium (o-Ps) into vacuum outside mesoporous silica films on glass is measured in reflection mode with a specially designed lifetime (LT) spectrometer. Values as high as 40% are found. The intensity of the 142 ns vacuum LT is recorded as a function of reemission depth. The LT depth profiling is correlated to the 2gamma and 3gamma energy ones to determine the annihilation characteristics inside the films. Positron lifetime in capped films is used to determine the pore size. For the first time, a set of consistent fingerprints for Ps annihilation, o-Ps reemission into vacuum, and pore size, is directly determined in CTACl-TEOS films.
• Vortex Redistribution below the First-Order Transition Temperature in the beta-Pyrochlore Superconductor KOs2O6
  
  • Shibauchi Takasada
  • Konczykowski Marcin
  • van Der Beek Cornelis Jacominus
  • Matsuda Yuji
  • Okazaki Ryuji
  • Yamaura Jinichi
  • Nagao Y.
  • Hiroi Zenji
  Physical Review Letters, American Physical Society, 2007, 99, pp.257001. A miniature Hall-sensor array was used to detect magnetic induction locally in the vortex states of the beta-pyrochlore superconductor KOs2O6. Below the first-order transition at Tp~8 K, which is associated with a change in the rattling motion of K ions, the lower critical field and the remanent magnetization both show a distinct decrease, suggesting that the electron-phonon coupling is weakened below the transition. At high magnetic fields, the local induction shows an unexpectedly large jump at Tp whose sign changes with position inside the sample. Our results demonstrate a novel redistribution of vortices whose energy is reduced abruptly below the first-order transition at Tp. (10.1103/PhysRevLett.99.257001)
  DOI : 10.1103/PhysRevLett.99.257001
• Trapped and transient radicals observed in ethylene–propylene–diene terpolymers
  
  • Esnouf Stéphane
  • Balanzat Emmanuel
  Polymer, Elsevier, 2007, 48, pp.7531. Radicals formed by irradiation by high energy electron in ethylene–propylene–hexadiene terpolymer (EP–HD) have been studied using electron spin resonance (ESR). Two methods were used to analyse the different radicals formed by irradiation: firstly, classical low temperature irradiations were carried out, secondly, rapid quenching in liquid nitrogen of the material after high dose rate irradiation. The feasibility and the efficiency of the latter method to observe short-lived radicals have been demonstrated. This type of experiment provides unique information concerning the rate of production and the rate of reaction of radicals (10.1016/j.polymer.2007.10.028)
  DOI : 10.1016/j.polymer.2007.10.028
• Ab-Initio Calculations of Many body effects in electronic spectre.
  
  • Gatti Matteo
  , 2007. Theoretical Spectroscopy has become a field of the most active research in physics of matter. It involves using the ab initio methods to comfortably give, for example, an interpretation of experimental spectra and to predict electronic and optical properties of new materials. The state of the art for the calculation of excited states is the result of a long history. It is based on the one hand, on the theory of density functional theory (DFT) [1] and its extension to potential time-dependent (TDDFT) and, secondly, the many-body theory, one example is the famous GW approximation [2]. In this context, the purpose of this thesis was, on the one hand, to study the application of common approximations of these methods (which were developed especially for semiconductors and simple metals) in the case of systems over correlated such as the oxides of transition metals. In particular, vanadium oxide is the paradigm of these systems. It is characterized by a phase transition metal-insulator, whose physical explanation was the topic of a debate that has lasted over forty years. We showed that a GW calculation is able to reproduce without using adjustable parameters, the electron correlation effects in band structure of both phases of vanadium oxide and the satellite in the photoemission spectrum of the metal [3 ]. On the other hand, as the study of these systems requires complex calculations increasingly heavy, we have considered in this thesis an alternative approach [4]. It is based on the introduction of an effective potential, local, real and dynamic (unlike the self-energy, appearing in the GW method, which is non-local and complex) for the calculation of quasiparticle energies, which are measured in a photoemission experiment. In particular, we studied the properties of this new potential in the case of model systems and we have sought approximations for the application to real systems.
• [Preoperative treatments of rectal cancers]
  
  • Bosset Jean-François
  • Nguyen F.
  • Bosset M.
  • Servagi-Vernat S.
  • Sedrati A.
  • Lorgis V.
  Cancer/Radiothérapie, Elsevier Masson, 2007, 11 (6-7), pp.349-352. Surgery alone is no longer appropriate to the treatment of T3-T4 resecable rectal cancer. Preoperative chemoradiotherapy has recently been approved as the new standard treatment. This approach improves local control with local failure rate raranging now around 6-8%. However, it does not impact on overall survival. It becomes urgent to develop new concepts and a basic research in the understanding of the biological mechanisms that may explain the resistance of the micrometastatic process. (10.1016/j.canrad.2007.08.005)
  DOI : 10.1016/j.canrad.2007.08.005
• Surface specific peptide immobilization on radiografted polymers as potential screening assays for antiangiogenic immunotherapy
  
  • Clochard M.-Cl
  • Cuscito O
  • Berthelot T
  • Betz N
  • Bittencourt C
  • Pireaux J.-J
  • Goncalves M
  • Gionnet K
  • Déléris G
  Reactive and Functional Polymers, Elsevier, 2007, pp.77. Angiogenesis is a key process of cancer development and metastasis. It's inhibition is an important and promising strategy to block tumor growth and invasion. One of these approaches, based on antiangiogenic immunotherapy, is the recognition of a specific region of an angiogenic growth factor, called VEGF-A, by monoclonal antibodies. Thus, we aimed to design a novel assay to screen potential monoclonal antibodies directed against VEGF-A. In a first approach, we chose to perform covalent coupling of angiogenesis active cyclopeptides onto biocompatible thermoplastic transparent PVDF films and to fully characterize the chemical structure, the surface state and the biochemical properties of the synthesized devices. Electron beam radiation created radical sites on PVDF films without adding any toxic chemicals. These primary radicals and some induced peroxides were used as initiators for acrylic acid polymerization. Under our experimental conditions, surface grafting was favoured. Functionalization of PVDF-g-PAA films with peptides via a spacer arm was possible by performing two subsequent coupling reactions. EDC was used as coupling agent. Spacer arm saturation of the film surface was achieved for 25 mol% yield meaning that one spacer arm on four carboxylic acids were covalently bound. Peptide immobilization resulted in binding 10 times less leading to a final 3 mol% yield. Binding densities are governed by their individual space requirements. Each chemical step has been followed by FTIR in ATR mode, NMR using HR MAS technique and XPS. From XPS results, a layer of peptide covered PVDF-g-PAA film surface. The amounts of covalently immobilized peptide were determined using indirect UV spectroscopy on supernatant reaction solution. Yields were correlated with high resolution NMR results. The peptide/antibody recognition validated our system showing the conservation of peptide tridimensional structure with a positive response to specific antibodies. Because of the covalent protein linkage to PVDF films, a simple cleaning with immunoaffinity chromatography buffer allows the films to be reused. (10.1016/j.reactfunctpolym.2007.10.017)
  DOI : 10.1016/j.reactfunctpolym.2007.10.017
• Efficient ab initio calculations of bound and continuum excitons
  
  • Sottile Francesco
  • Marsili Marherita
  • Olevano Valerio
  • Reining Lucia
  Physical Review B: Condensed Matter and Materials Physics (1998-2015), American Physical Society, 2007, 76 (16), pp.161103(R). We present calculations of the absorption spectrum of semiconductors and insulators comparing various approaches: (i) the two-particle Bethe-Salpeter equation of Many-Body Perturbation Theory; (ii) time-dependent density-functional theory using a recently developed kernel that was derived from the Bethe-Salpeter equation; (iii) a scheme that we propose in the present work and that allows one to derive different parameter-free approximations to (ii). We show that all methods reproduce the series of bound excitons in the gap of solid argon, as well as continuum excitons in semiconductors. This is even true for the simplest static approximation, which allows us to reformulate the equations in a way such that the scaling of the calculations with number of atoms equals the one of the Random Phase Approximation. (10.1103/PhysRevB.76.161103)
  DOI : 10.1103/PhysRevB.76.161103
• Ponderomotive effects in the femtosecond plasmon-assisted photoelectric effect in bulk metals: Evidence for coupling between surface and interface plasmons
  
  • Raynaud Michèle
  • Kupersztych Joseph
  Physical Review B: Condensed Matter and Materials Physics (1998-2015), American Physical Society, 2007. The existence of ponderomotive acceleration effects in the metal bulk has been experimentally demonstrated in the context of the femtosecond plasmon-assisted multiphoton photoelectric effect in metal systems. The resulting electron energy spectra show that these effects essentially depend on the coupling between the surface and interface plasmons. While the essential part played by the ponderomotive force of the surface plasmon is to accelerate the photoelectrons in the vacuum, the dramatic enhancement of the photoelectron production and the angular dependence in the photoemission process mainly result from ponderomotive effects in the metal bulk. In the photoelectric effect in metals, photoelectrons may be emitted from a region near the metal surface 1,2 or may originate from the bulk. 3 In the bulk, electron excitation occurs via photon absorption in the presence of a third body ͑ion or impurity͒ or through interband transitions. On the other hand, the surface effects play an essential role for the number of electrons emitted while the absorption of light energy in the surface layer ͑a few nanometers͒ is relatively small ͑about 0.1% of the total absorption rate͒. In recent years, much attention has been paid to the possibility of enhancing electron emission of metals through the surface pho-toelectric effect by means of light excitation of electron collective oscillation modes localized near the metal surface. 4 (10.1103/PhysRevB.76.241402)
  DOI : 10.1103/PhysRevB.76.241402
• Primary nucleation processes in binary oxide growth: The case of MgO
  
  • Geneste Grégory
  • Morillo Joseph
  • Finocchi Fabio
  • Hayoun Marc
  Surface Science : A Journal Devoted to the Physics and Chemistry of Interfaces, Elsevier, 2007, 601, pp.5616–5627. The smallest forms of stoichiometric and non-stoichiometric MgO clusters appearing on the MgO(001) surface during the growth under atomic and/or molecular deposition are investigated from first-principles and empiric potentials. The basic entities (MgO molecule and (MgO)2 cluster) result from a very exoenergetic and spontaneous redox reaction that involves directly the deposited species (Mg and O atoms, O2 molecule). The stoichiometric clusters, resulting from the agglomeration of MgO molecules, are very stable under non-polar forms. Their formation energy is modelized, down to very small sizes, within an independent defect model. We point out the specificity of such clusters in the framework of the classical nucleation theory. The high-energy polar isomers are associated to destabilizing macroscopic electric fields and dipoles. These forms may nevertheless be strongly stabilized by incorporating extra Mg adatoms that give part of their valence shell to the cluster and decrease the total dipole in this way, illustrating the delicate coupling between chemistry and electrostatics in growth processes of oxides. Based on these considerations, we propose a scenario describing MgO growth both in the step-flow and in the nucleation regime. (10.1016/j.susc.2007.09.051)
  DOI : 10.1016/j.susc.2007.09.051
• Liquid metals for nuclear applications
  
  • Gorse-Pomonti Dominique
  • Russier Vincent
  Journal of Non-Crystalline Solids, Elsevier, 2007, 353 (32-40), pp.3600-3614. Nuclear applications of liquid metals concern waste transmuters and liquid metal cooled fast reactors of Generation IV. One section of this paper is devoted to a short review of the motivations for liquid metals as reactor coolant or spallation target material and to historic aspects. The next two sections are dedicated to the neutron and physical properties of liquid metals, with special emphasis on sodium, lead and lead–bismuth eutectic, their respective advantages and drawbacks as reactor coolants. The question of the structure of liquid metals in relation with the liquid metal coolant technology is briefly addressed. The last section concerns the compatibility of structural materials with sodium, lead and lead–bismuth eutectic, with attention being paid to the impurities control in the different cases. We conclude briefly. (10.1016/j.jnoncrysol.2007.05.175)
  DOI : 10.1016/j.jnoncrysol.2007.05.175
• In-plane field induced vortex liquid correlations in underdoped Bi_2Sr_2CaCu_2O_8+\delta
  
  • Spathis Panayotis
  • Konczykowski Marcin
  • Gierlowski Piotr
  • Li Ming
  • Kes Peter H.
  • van Der Beek Cornelis Jacominus
  Physical Review B: Condensed Matter and Materials Physics (1998-2015), American Physical Society, 2007, 76, pp.104518. By measuring the microwave dissipation in the vicinity of the Josephson Plasma Resonance, we have probed the influence of an in-plane magnetic field on pancake vortex correlations along the c-axis in underdoped Bi$_2$Sr$_2$CaCu$_2$O$_{8+\delta}$ ($T_c=72.4 \pm 0.6$ K) single crystals both in the vortex liquid and in the vortex solid phase. The in-plane field enhances the interlayer phase coherence in the liquid state, close to the melting line, but slightly depresses it in the solid state. We interpret this as the result of an attractive force between pancake vortices and Josephson vortices, apparently also present in the vortex liquid state. The results unveil a boundary between a correlated vortex liquid in which pancakes adapt to Josephson vortices, and the usual homogeneous liquid. (10.1103/PhysRevB.76.104518)
  DOI : 10.1103/PhysRevB.76.104518
• Nanoporous beta-PVDF membranes with selectively functionalized pores
  
  • Cuscito Olivia
  • Clochard M.C.
  • Esnouf Stéphane
  • Betz Natacha
  • Lairez Didier
  Nuclear Instruments and Methods in Physics Research Section B: Beam Interactions with Materials and Atoms, Elsevier, 2007, 265, pp.309-313. Poly (vinylidene fluoride) ( -PVDF) nanoporous membranes are obtained by heavy ion irradiation and track etching leading to cylindrical pores. Pores diameter measured by Scanning Electron Microscopy and Small Angle Neutron Scattering lies in the 20-50nm range. Electron Paramagnetic Resonance study gives evidence that radicals still remains in PVDF membrane after track-etching. These radicals allows acrylic acid polymerization to be initiated onto membrane. So radiografted and functionalized membranes are characterized using Infrared Spectroscopy, weighing measurements and Energy Dispersive Spectroscopy. Finally, radiografted poly(acrylic-acid) (PAA) has been selectively labeled by fluorophores and imaged by Confocal Laser Scanning Microscopy. Images show the localisation of PAA specifically inside nanopores. (10.1016/j.nimb.2007.08.089)
  DOI : 10.1016/j.nimb.2007.08.089
• Influence of asymmetric etching on ion track shapes in polycarbonate
  
  • Clochard M.-C
  • L Wade Travis
  • Wegrowe J.-E
  • Balanzat Emmanuel
  Nuclear Instruments and Methods in Physics Research Section B: Beam Interactions with Materials and Atoms, Elsevier, 2007, 265 (1), pp.325-329. By combining low-energy ion irradiation with asymmetric etching, conical nanopores of controlled geometry can be etched in poly-carbonate (PC). Cone bases vary from 0.5 to 1 lm. Top diameters down to 17 nm are reached. When etching from one side, the pH on the other side (bathed in neutral or acidic buffer) was monitored. Etching temperature ranged from 65 °C to 80 °C. Pore shape characterization was achieved by electro replication combined with SEM observation. The tip shape depended on whether an acidic buffer was used or not on the stopped side. (10.1016/j.nimb.2007.08.065)
  DOI : 10.1016/j.nimb.2007.08.065
• New conductive copolymer membranes via track-etched PC templates for biological media ultra-filtration
  
  • Berthelot T.
  • Baudin C.
  • Balanzat E.
  • Clochard M.C.
  Nuclear Instruments and Methods in Physics Research Section B: Beam Interactions with Materials and Atoms, Elsevier, 2007, 265, pp.320-324. New microstructurated copolymer membranes have been synthesized using a track-etched polycarbonate (PC) matrix. These membranes proved to be an important device in the field of ultra-filtration and synthetic membranes. These novel structures were obtained by irradiating at various angles (+30 , 30 ). Such architecture is expected to improve not only the exchange properties but also, the behaviour under high flow pressure during their use as nanofiltration membranes. Membrane functionalization was performed with an amino acid as a simple biological model. Transmission and ATR-FTIR spectroscopies show that the doping state of copolymer dramatically influences the amino acid coupling rate. UV-vis spectroscopy indicates that the copolymer may be self-doped. (10.1016/j.nimb.2007.08.066)
  DOI : 10.1016/j.nimb.2007.08.066
• Dynamic and Thermodynamic Properties of Porous Vortex Matter in Bi2Sr2CaCu2O8 in an Oblique Magnetic Field
  
  • Avraham Nurit
  • Goldschmidt Yadin
  • Liu Jintao
  • Myasoedov Yuri
  • Rappaport Michael
  • Zeldov Eli
  • van Der Beek Cornelis Jacominus
  • Konczykowski Marcin
  • Tamegai Tsuyoshi
  Physical Review Letters, American Physical Society, 2007, 99, pp.087001. Vortex matter in Bi2Sr2CaCu2O8 with a low concentration of tilted columnar defects (CDs) was studied using magneto-optical measurements and molecular dynamics simulations. It is found that while the dynamic properties are significantly affected by tilting the magnetic field away from the CDs, the thermodynamic transitions are angle independent. The simulations indicate that vortex pancakes remain localized on the CDs even at large tilting angles. This preserves the vortex thermodynamics, while vortex pinning is considerably weakened due to kink sliding. (10.1103/PhysRevLett.99.087001)
  DOI : 10.1103/PhysRevLett.99.087001
• Transforming nonlocality into frequency dependence: a shortcut to spectroscopy
  
  • Gatti Matteo
  • Olevano Valerio
  • Reining Lucia
  • Tokatly Ilya V.
  Physical Review Letters, American Physical Society, 2007, 99 (5), pp.057401. Measurable spectra are theoretically very often derived from complicated many-body Green's functions. In this way, one calculates much more information than actually needed. Here we present an in principle exact approach to construct effective potentials and kernels for the direct calculation of electronic spectra. In particular, the potential that yields the spectral function needed to describe photoemission turns out to be dynamical but {\it local} and {\it real}. As example we illustrate this ''photoemission potential'' for sodium and aluminium, modelled as homogeneous electron gas, and discuss in particular its frequency dependence stemming from the nonlocality of the corresponding self-energy. We also show that our approach leads to a very short derivation of a kernel that is known to well describe absorption and energy-loss spectra of a wide range of materials. (10.1103/PhyRevLett.99.057401)
  DOI : 10.1103/PhyRevLett.99.057401
• b-Irradiation Effect in Aluminoborosilicate Glasses: The Role of RE Codoping (RE= Sm, Gd)
  
  • Malchukova Evguenia
  • Boizot Bruno
  , 2008, 50 (9), pp.1687-1691. The effect of Sm and Gd codoping on the structural modifications of β-irradiated aluminoborosilicate glasses has been studied by electron paramagnetic resonance (EPR) and Raman spectroscopy. The EPR spectra showed that the relative amount of Gd3+ ions occupying network former positions ( ) follows a nonlinear behavior as a function of the Sm/Gd ratio. This suggests that codoping favors the occupation by Gd3+ ions of the network former positions rather than the modifier positions in aluminoborosilicate glasses. The appearance of a superhyperfine structure of EPR lines attributed to boron–oxygen hole centers (BOHC) with increasing Sm/Gd ratio was observed. This suggests that Gd3+ ions are diluted in the vicinity of the BOHC defects. The concentration of defects created by irradiation reveals a nonlinear dependence on Sm and Gd codoping for the lowest irradiation dose (105 Gy). Therefore, codoping also affects the defect creation processes at least at the lowest irradiation dose. Raman spectroscopy measurements suggest that the irradiation-induced structural changes vary nonlinearly with the Sm/Gd ratio. In fact, the shift of the Si–O–Si bending vibration modes reveals a clear minimum for samples containing equal amounts of Sm and Gd (1 : 1) in the investigated glasses. (10.1134/S1063783408090205)
  DOI : 10.1134/S1063783408090205
• Interaction photon/matière : de la photochimie aux photosciences. 1ère partie : La photochimie pour mieux vivre
  
  • Tran-Thi T.-H.
  • Amouyal E.
  , 2007, pp.100.
• Role of self-irradiation defects on the ageing of 239PuCoGa5
  
  • Jutier Frédéric
  • Griveau Jean-Christophe
  • van Der Beek Cornelis Jacominus
  • Colineau Eric
  • Wastin Franck
  • Rebizant Jean
  • Boulet Pascal
  • Wiss Thierry
  • Thiele Hartmut
  • Simoni Eric
  EPL - Europhysics Letters, European Physical Society / EDP Sciences / Società Italiana di Fisica / IOP Publishing, 2007, 78, pp.57008. Low-temperature accumulation and annealing experiments, in conjunction with electrical resistivity and critical current density measurements, were used to study the ageing of the actinide superconductor PuCoGa5. These measurements reveal that 2-nm sized non-superconducting point-like regions are the main damage formed during room temperature ageing; smaller point-like defect were irrelevant to transport properties. Defect sizes and densities deduced from experiment agree with Transmission Electron Micoscopy observations. (10.1209/0295-5075/78/57008)
  DOI : 10.1209/0295-5075/78/57008
• Optical properties of real surfaces: Local-field effects at oxidized Si(100)(2x2) computed with an efficient numerical scheme
  
  • Caramella L.
  • Onida G.
  • Finocchi F.
  • Reining L.
  • Sottile F.
  Physical Review B: Condensed Matter and Materials Physics (1998-2015), American Physical Society, 2007, 75 (20), pp.205405. We show the application of an efficient numerical scheme to obtain the independent-particle dynamic polarizability matrix chi((0))(r,r('),omega), a key quantity in modern ab initio excited-state calculations. The method has been applied to the study of the optical response of a realistic oxidized silicon surface, including the effects of crystal local fields. The latter are shown to substantially increase the surface optical anisotropy in the energy range below the bulk band gap. Our implementation in a large-scale ab initio computational code allows us to make a quantitative study of the CPU time scaling with respect to the system size, and demonstrates the real potential of the method for the study of excited states in large systems. (10.1103/PhysRevB.75.205405)
  DOI : 10.1103/PhysRevB.75.205405
• Vortex liquid correlations induced by in-plane field in underdoped Bi2Sr2CaCu2O8+d460-462
  
  • Spathis Panayotis
  • Konczykowski Marcin
  • van Der Beek Cornelis Jacominus
  • Gierlowski Piotr
  • Li Ming
  • Kes Peter H.
  , 2007, 460-462, pp.1218-1219. By measuring the Josephson Plasma Resonance, we have probed the influence of an in-plane magnetic field on the pancake vortex correlations along the c-axis in heavily underdoped Bi2Sr2CaCu2O8+d (Tc = 72.4 +/- 0.6 K) single crystals both in the vortex liquid and in the vortex solid phase. Whereas the in-plane field enhances the interlayer phase coherence in the liquid state close to the melting line, it slightly depresses it in the solid state. This is interpreted as the result of an attractive force between pancake vortices and Josephson vortices, apparently also present in the vortex liquid state. The results unveil a boundary between a correlated vortex liquid in which pancakes adapt to Josephson vortices, and the usual homogeneous liquid. (10.1016/j.physc.2007.04.053)
  DOI : 10.1016/j.physc.2007.04.053
• Raman bands of double-wall carbon nanotubes: comparison with single- and triple-wall carbon nanotubes, and influence of annealing and electron irradiation
  
  • Puech Pascal
  • Flahaut Emmanuel
  • Bassil Ayman
  • Juffmann Thomas
  • Beuneu François
  • Bacsa Wolfgang
  Journal of Raman Spectroscopy, Wiley, 2007, 38 (6), pp.714-720. We compare the G and G2D bands of single-, double- and triple-wall carbon nanotubes (CNTs). We observe that the band shape is sensitive to the number of walls of the CNTs. For single-wall carbon nanotubes (SWCNTs), the G band is composed of two distinct contributions G+ and G-, while the G band for double-wall nanotubes is composed of one band with two main contributions from the inner and the outer tube. The G2D band can be fitted with one Lorentzian for single-wall tubes, while two distinct contributions are observed for double-wall carbon nanotubes (DWCNTs). Considerable variations of the G2D band are found with similar first order Raman spectra. Annealing influences the D- and RBM-band intensities. Electron irradiation has the effect of decreasing the G- and D-band wavenumbers but does not enhance the D-band intensity considerably. The down-shifts of the G- and D-band wavenumbers are correlated and are the same for two excitation wavelengths. This is consistent with the scattering of phonons around the K-point. (10.1002/jrs.1690)
  DOI : 10.1002/jrs.1690
• Fully anisotropic superconducting transition in ion irradiated YBa2Cu3O7−delta with a tilted magnetic field
  
  • Espinosa-Arronte Beatriz
  • Andersson Magnus
  • van Der Beek Cornelis Jacominus
  • Nikolaou Marios
  • Lidmar Jack
  • Wallin Mats
  Physical Review B: Condensed Matter and Materials Physics (1998-2015), American Physical Society, 2007, 75, pp.100504. We consider the superconducting vortex solid-to-liquid transition in heavy ion-irradiated untwinned YBa2Cu3O7−delta single crystals in the case where the magnetic field direction does not coincide with that of the irradiation-induced linear columnar defects. For a certain range of angles, the resistivities measured in three orthogonal spatial directions vanish at the transition as three clearly different powers of reduced temperature. This is in contrast to the usual isotropic scaling of physical quantities close to a continuous phase transition, and to the Bose glass transition occurring for field parallel to the columns, where the scaling is anisotropic in one direction. Thus, our findings yield evidence for a new type of critical behavior with fully anisotropic critical exponents. 1 (10.1103/PhysRevB.75.100504)
  DOI : 10.1103/PhysRevB.75.100504
• Thermodynamics of a heavy-ion-irradiated superconductor: The zero-field transition
  
  • van Der Beek Cornelis Jacominus
  • Klein Thierry
  • Brusetti René
  • Marcenat C.
  • Wallin Mats
  • Teitel Stephen
  • Weber Hans
  Physical Review B: Condensed Matter and Materials Physics (1998-2015), American Physical Society, 2007, 75, pp.100501. Specific heat measurements show that the introduction of amorphous columnar defects considerably affects the transition from the normal to the superconducting state in {\em zero} magnetic field. Experimental results are compared to numerical simulations of the 3D XY model for both the pure system and the system containing random columnar disorder. The numerics reproduce the salient features of experiment, showing in particular that the specific heat peak changes from cusp-like to smoothly rounded when columnar defects are added. By considering the specific heat critical exponent $\alpha$, we argue that such behavior is consistent with recent numerical work [A. Vestergren et al., Phys. Rev. B {\bf 70}, 054508 (2004)] showing that the introduction of columnar defects changes the universality class of the transition. (10.1103/PhysRevB.75.100501)
  DOI : 10.1103/PhysRevB.75.100501