Publications

2012

• Effects of disorder in iron-based superconductors
  
  • Demirdis Sultan
  , 2012. The pinning of vortices is used as a probe for the identification of disorder and its effect on superconductivity in 122-type iron-based superconductors. Using a new analysis method taking into account the interaction of individual vortices with their neighbors, pinning energies and pinning forces in Ba(Fe1-xCox)2As2 are extracted from the vortex distributions in the regime of small fields. The correlation of measurements of the critical current density Jc with the spatial distribution of vortices shows that pinning in this particular regime is due to the heterogeneity of superconducting properties, on the scale of 20-100 nm. Application of the same analysis procedure on the vortex structure in BaFe2(As1-xPx)2 with less density fluctuations, shows that the pinning forces and energies depend on the doping level x. Both Jc measurements and pinning force distributions independently yield a mean distance between pinning centers of about 90 nm, increasing with increasing P-content x. Combination of the above results and critical current density measurements lead to the conclusion that the low field plateau observed in Jc curves, followed by a power-law decrease, emerges from strong pinning due to nm scale heterogeneity of superconducting properties. Attention is also paid to the weak collective pinning contribution that manifests itself at higher fields > 1 T. Notably, this contribution is consistently analyzed in terms of quasiparticle scattering and mean free path fluctuations. In order to test this premise irradiation of Co, Ni and P-doped 122-type iron-based compounds with high-energy 2.5 MeV electrons is performed for several doping levels of the materials and to different doses. Such irradiation introduces atomic sized point-like defects. Following irradiation it appears that the critical temperature Tc shows a similar depression for all studied materials. The weak collective contribution to Jc in Co-doped is found to clearly increase. Moreover this contribution appears after irradiation of the P-doped compound in which it was previously absent. This allows one to confirm the role of atomic point-like pins as scatterers in Ni and Co-doped compounds, as well as the hypothesis that these defects are at the origin of the weak collective pinning contribution to Jc at larger fields.
• Low-frequency Raman scattering under high pressure in diamond anvil cell: Experimental protocol and application to GeO2 and SiO2 boson peaks
  
  • Deschamps T.
  • Martinet C.
  • de Ligny D.
  • Bruneel J.L.
  • Champagnon B.
  Journal of Non-Crystalline Solids, Elsevier, 2012, 358 (23), pp.3156-3160. Low frequency vibrations, a universal feature of amorphous solids which is responsible for thermodynamical anomalies at low temperature, are complicated to record in high pressure device, notably because of the closeness of the elastic line. We first present an experimental protocol allowing to record the in situ low-frequency Raman scattering of samples under high pressure in the diamond anvil cell apparatus with a high quality. This protocol is particularly adapted to study the evolution of the boson peak of glassy materials. The second part is dedicated to the study of the boson peak of a-GeO2, a typical strong glass. The results, which clearly show the non-Debye behaviour of this material at the beginning of the compression where an anomalous compression takes place, are compared to previous measurements on a-SiO2. Interpretation in terms of local structural transitions and discussions about the elastic nanoheterogeneities of the amorphous state are addressed. (10.1016/j.jnoncrysol.2012.08.021)
  DOI : 10.1016/j.jnoncrysol.2012.08.021
• Low-energy excitations in strongly correlated materials: A theoretical and experimental study of the dynamic structure factor in V2O3
  
  • Iori Federico
  • Rodolakis Fanny
  • Gatti Matteo
  • Reining Lucia
  • Upton M.
  • Shvyd'Ko Y. V.
  • Rueff Jean-Pascal
  • Marsi M.
  Physical Review B: Condensed Matter and Materials Physics (1998-2015), American Physical Society, 2012, 86, pp.205132.
• Étude de vitrocéramiques modèles riches en CaMoO4 pour le confinement de déchets nucléaires
  
  • Taurines Tatiana
  , 2012. L'oxyde de molybdène est peu soluble dans les verres borosilicatés et peut entrainer la cristallisation de phases molybdates lors du retraitement de combustibles riches en Mo ou lorsque le taux de charge en produits de fission et actinides mineurs est élevé. Le contrôle de cette cristallisation est primordial pour garantir les propriétés de confinement des matrices. Cette thèse est consacrée à l'étude de vitrocéramiques modèles riches en phase powellite (CaMoO4) obtenues par traitements thermiques à partir d'un verre nucléaire simplifié dans le système SiO2 - B2O3 - Na2O- CaO - Al2O3 - MoO3 - TR2O3 (TR = Gd, Eu, Nd). Les terres rares (TR) sont ajoutées en tant que simulants d'actinides mineurs trivalents et comme sondes spectroscopiques. L'influence des teneurs en MoO3 et TR2O3 sur la cristallisation de la powellite a été étudiée. Une large gamme de vitrocéramiques biphasées (verre résiduel similaire + powellite) avec des tailles de cristaux variées a été obtenue. Lorsque la teneur en MoO3 est supérieure ou égale à 2.5 %mol, une séparation de phase liquide-liquide a lieu pendant la trempe. Nous avons montré, que l'ajout de terres rares inhibe la séparation de phase liée au molybdène mais entraine une décomposition spinodale du verre résiduel. La cristallisation d'un verre complexe et l'insertion des terres rares dans la structure powellite ont également été étudiées. L'influence de la microstructure des vitrocéramiques sur la création de défauts ponctuels et sur les évolutions structurales sous excitation électronique (irradiations β) a enfin été considérée. Dans ce travail, nous avons montré que la résistance aux excitations électroniques des vitrocéramiques est contrôlée par celle du verre résiduel.
• Titanium and zirconium oxidation under argon irradiation in the low MeV range
  
  • Gorse-Pomonti Dominique
  • Do Ngoc-Long
  • Bererd Nicolas
  • Moncoffre Nathalie
  • Baldinozzi Gianguido
  , 2013, 1514, pp.81-85. We studied the irradiation effects on Ti and Zr surfaces in slightly oxidizing environment (rarefied dry air, 500°C) using multi-charged argon ions in the low MeV range (1 - 9 MeV) to the aim of determining the respective role of the electronic and nuclear stopping power in the operating oxidation process under irradiation. We have shown that ballistic collisions contribute significantly to the enhanced Ti and Zr oxidation under MeV argon bombardment. We have also shown that the projectile energy plays a significant role in the overall process. A significant oxide film thickening is visible on titanium under irradiation, taking the form of a well-defined oxidation peak between 1 and 4 MeV, as a result of the Nuclear Backscattering Spectroscopy and Spectroscopic Ellipsometry studies. A significant oxide film thickening is also visible on zirconium under same irradiation conditions, at 4 and 9 MeV, as a result of the NBS study. Work is in progress in order to determine how the modified oxidation process depends in this case on the projectile energy. (10.1557/opl.2013.127)
  DOI : 10.1557/opl.2013.127
• Etude de l'oxydation thermique du titane et du zirconium sous irradiation aux ions d'argon dans le domaine du MeV (E ≤ 15 MeV)
  
  • Do Ngoc-Long
  , 2012. Nous avons montré que l'irradiation aux ions d'argon d'énergie comprise entre 1 et 15 MeV cause des dommages en surface du titane et du zirconium, qui prennent la forme d'une oxydation accélérée et/ou d'une cratérisation dont les effets évoluent en fonction de l'énergie du projectile et de l'atmosphère de recuit (température et pression), simulant les conditions environnementales représentatives de l'interface gaine/combustible d'un réacteur REP. Par AFM, nous avons montré que la surface du titane et du zirconium était attaquée par bombardement aux ions d'argon, à haute température (jusqu'à 500°C) en milieu faiblement oxydant (sous pression d'air sec raréfié comprise entre 5,7 10-5 Pa et 5 10-3 Pa) et à une dose moyenne fixée à environ 5 1014 ions.cm-2. On observe ainsi la formation de cratères nanométriques sur toute la surface du titane irradié entre 2 et 9 MeV et celle du zirconium irradié à 4 MeV, dont les caractéristiques varient en fonction de la température et de la pression. Dans le cas du couple Ar/Ti, l'efficacité d'endommagement superficiel augmente lorsque l'énergie du projectile diminue de 9 à 2 MeV. Par ailleurs, alors que la surface du titane apparaît transparente au faisceau d'ions à 15 MeV, celle du zirconium révèle de nombreux cratères micrométriques entourés d'un large halo sombre. Les caractéristiques des cratères (taille et densité superficielle) diffèrent de façon significative de celles observées à la fois dans le domaine des basses énergies (keV) où le dépôt d'énergie est contrôlé par les collisions balistiques (Sn) et dans le domaine des hautes énergies (MeV - GeV) où le dépôt d'énergie est contrôlé par les excitations électroniques (Se), ce qui n'était pas complètement inattendu dans le domaine d'énergie intermédiaire étudié, dans lequel des effets de pouvoir d'arrêt combiné Sn - Se sont envisageables. Par XPS couplé au décapage ionique, nous avons montré qu'il existe un effet d'irradiation sur l'oxydation thermique du titane, exacerbée sous faisceau d'ions d'argon entre 2 et 9 MeV, et qu'il existe aussi un effet d'énergie sur l'épaisseur et la stœchiométrie de l'oxyde. L'étude menée par Ellipsométrie Spectroscopique sur les films d'oxyde formés entre 1 et 9 MeV a corroboré ces résultats et montré précisément qu'il existe un pic d'oxydation en fonction de l'énergie d'ions d'argon, qui présente un maximum à 3 MeV, dans les conditions de l'expérience. Les mesures de gain d'oxygène effectuées par NBS confirment l'existence de ce pic d'oxydation. Les résultats acquis à ce jour par NBS concernant l'oxydation thermique du zirconium sous irradiation à l'argon de 4 et 9 MeV confirment les travaux antérieurs du groupe Aval du Cycle Electronucléaire de l'Institut de Physique Nucléaire de Lyon, et suggèrent fortement l'existence d'un pic d'oxydation dans la même plage d'énergie de projectile que pour le titane.
• Low-energy excitations in strongly correlated materials: A theoretical and experimental study of the dynamic structure factor in V2O3
  
  • Iori Federico
  • Rodolakis Fanny
  • Gatti Matteo
  • Reining Lucia
  • Upton M.
  • Shvyd'Ko Y.
  • Rueff Jean-Pascal
  • Marsi Marino
  Physical Review B, American Physical Society, 2012, 86 (20), pp.205132. (10.1103/PhysRevB.86.205132)
  DOI : 10.1103/PhysRevB.86.205132
• Giant Anisotropy of Spin-Orbit Splitting at the Bismuth Surface
  
  • Ohtsubo Y.
  • Mauchain Julien
  • Faure Jérôme
  • Papalazarou E.
  • Marsi M.
  • Le Fèvre P.
  • Bertran F.
  • Taleb-Ibrahimi A.
  • Perfetti L.
  Physical Review Letters, American Physical Society, 2012, 109 (22), pp.226404. We investigate the bismuth (111) surface by means of time and angle resolved photoelectron spectroscopy. The parallel detection of the surface states below and above the Fermi level reveals a giant anisotropy of the spin-orbit spitting. These strong deviations from the Rashba-like coupling cannot be treated in k·p perturbation theory. Instead, first principles calculations could accurately reproduce the experimental dispersion of the electronic states. Our analysis shows that the giant anisotropy of the spin-orbit splitting is due to a large out-of plane buckling of the spin and orbital texture. (10.1103/PhysRevLett.109.226404)
  DOI : 10.1103/PhysRevLett.109.226404
• Ab initio study of defective chains in icosahedral boron carbide B4C
  
  • Betranhandy Emmanuel
  • Vast Nathalie
  • Sjakste Jelena
  Solid State Sciences, Elsevier, 2012, 14 (11-12), pp.1683-1687. (10.1016/j.solidstatesciences.2012.07.002)
  DOI : 10.1016/j.solidstatesciences.2012.07.002
• Dynamical correlation in solids: a perspective in photoelectron spectroscopy
  
  • Guzzo Matteo
  , 2012. My thesis fits into the domain of theoretical spectroscopy. This term describes a set of theoretical approaches that go hand-in-hand with several experimental techniques such as optical absorption and reflectivity, inelastic X-ray scattering (IXS), electron energy-loss spectroscopy (EELS) and photoelectron (or photoe- mission) spectroscopy. This set of ab-initio theories is used to simulate, study, predict and understand what is and will be seen in experiment. These spectro- scopies are all connected to the dielectric function ε(ω ) of an electronic system which is, in fact, a fundamental quantity in many modern electronic structure theories. In particular I focused my research on photoemission spectroscopy, where the dielectric function enters as the screening of the hole due to the sys- tem. During my thesis I have worked on the development of new theoretical approaches, the aim of my project being to go beyond state-of-the-art meth- ods used in electronic structure calculations. These methods stem mainly from two larger theoretical frameworks: Time-Dependent Density-Functional The- ory (TDDFT) and Green's function theory -- also known as Many-Body Pertur- bation Theory (MBPT). I carried on the theoretical development in parallel with numerical simulations on real materials and with experimental measurements, performed to verify the reliability of theory.
• In situ Raman monitoring of materials under irradiation: study of uranium dioxide alteration by water radiolysis
  
  • Canizares A.
  • Guimbretière G.
  • Tobon A.
  • Raimboux N.
  • Omnée R.
  • Perdicakis M.
  • Muzeau B.
  • Leoni E.
  • Alam M. Shahanoor
  • Mendes E.
  • Simon D.
  • Matzen G.
  • Corbel C.
  • Barthe M.
  • Simon P.
  Journal of Raman Spectroscopy, Wiley, 2012, 43 (10), pp.1492-1497. In situ Raman scattering studies allow following real‐time evolutions of volume or surface structures under extreme conditions. In nuclear materials sciences, ion irradiation‐induced atomic organization modification and water radiolysis are of a major interest. In order to better understand these phenomena, we have developed an in situ versatile portable Raman spectroscopy system coupled with a cyclotron accelerator, allowing monitoring of a solid/liquid interface under irradiation and thus giving access to effects of radiolysis. The different parts of the system and their improvements are described in details. The system efficiency is highlighted by a comparative study of the time dependence of UO2 surface modification induced, on one hand by contact with water under irradiation by 5 MeV He2+ particles, and on the other hand by pure chemical alteration, through contact with a hydrogen peroxide solution. (10.1002/jrs.4088)
  DOI : 10.1002/jrs.4088
• Progressive transformations of silica glass upon densification
  
  • Sonneville C.
  • Mermet A.
  • Champagnon B.
  • Martinet C.
  • Margueritat J.
  • de Ligny D.
  • Deschamps T.
  • Balima Félix
  The Journal of Chemical Physics, American Institute of Physics, 2012, 137 (12), pp.124505. The elastic and plastic behaviors of silica glasses densified at various maximum pressure reached (12 GPa, 15 GPa, 19 GPa, and 22 GPa), were analyzed using in situ Raman and Brillouin spectroscopies. The elastic anomaly was observed to progressively vanish up to a maximum pressure reached of 12 GPa, beyond which it is completely suppressed. Above the elastic anomaly the mechanical behavior of silica glass, as derived from Brillouin measurements, is interpreted in terms of pressure induced transformation of low density amorphous silica into high density amorphous silica. (10.1063/1.4754601)
  DOI : 10.1063/1.4754601
• Low-energy silicon allotropes with strong absorption in the visible for photovoltaic applications
  
  • Botti Silvana
  • Flores-Livas Jose A.
  • Amsler Maximilian
  • Goedecker Stefan
  • Marques Miguel A. L.
  Physical Review B: Condensed Matter and Materials Physics (1998-2015), American Physical Society, 2012, 86, pp.121204. (10.1103/PhysRevB.86.121204)
  DOI : 10.1103/PhysRevB.86.121204
• Plasmon satellites in valence-band photoemission spectroscopy
  
  • Guzzo Matteo
  • Kas Joshua J.
  • Sottile Francesco
  • Silly Mathieu G.
  • Sirotti Fausto
  • Rehr John J.
  • Reining Lucia
  The European Physical Journal B: Condensed Matter and Complex Systems, Springer-Verlag, 2012, 85, pp.324.
• Efficient calculation of the polarizability: a simplified effective-energy technique
  
  • Berger Arjan
  • Reining Lucia
  • Sottile Francesco
  The European Physical Journal B: Condensed Matter and Complex Systems, Springer-Verlag, 2012, 85, pp.326. In a recent publication [J.A. Berger, L. Reining, F. Sottile, Phys. Rev. B 82, 041103(R) (2010)] we introduced the effective-energy technique to calculate in an accurate and numerically efficient manner the GW self-energy as well as the polarizability, which is required to evaluate the screened Coulomb interaction W. In this work we show that the effective-energy technique can be used to further simplify the expression for the polarizability without a significant loss of accuracy. In contrast to standard sum-over-state methods where huge summations over empty states are required, our approach only requires summations over occupied states. The three simplest approximations we obtain for the polarizability are explicit functionals of an independent- or quasi-particle one-body reduced density matrix. We provide evidence of the numerical accuracy of this simplified effective-energy technique as well as an analysis of our method. (10.1140/epjb/e2012-30237-5)
  DOI : 10.1140/epjb/e2012-30237-5
• Crystalline and magnetic anisotropy of the 3d-transition metal monoxidesMnO, FeO, CoO, and NiO
  
  • Schrön A.
  • Rödl Claudia
  • Bechstedt Friedhelm
  Physical Review B: Condensed Matter and Materials Physics (1998-2015), American Physical Society, 2012, 86, pp.115134.
• High Intensity Laser-Plasma Grating Interaction: surface wave excitation and particle acceleration
  
  • Alessandra Bigongiari
  , 2012. Surface waves in solids were first observed by Wood in 1902 as an anomaly in the diffraction of a continuous light source from a metal grating: the diffracted spectrum presented dark lines corresponding to certain wavelengths, which were later explained (Fano, 1941) in terms of the excitation of a surface wave sustained by the grating. Similarly to the metal grating case, a surface plasma wave (SPW) can be resonantly excited by a laser pulse at the surface of a laser-produced over-dense plasma, if the correct matching conditions are provided. SPWs propagate along the plasma-vacuum interface and are characterized by a localized, high frequency, resonant electric field. In the present work we describe numerically the dynamics of the plasma and the field distribution associated to SPW excitation, using two-dimensional particle-in-cell (PIC) simulations, where the plasma surface is initially pre-formed so that the SPW excitation conditions are fulfilled. We examine the surface wave excitation for a large range of laser intensities (Iλ2 =10^15-10^20 μm^2/Wcm^2) in order to study the transition from the non-relativistic to the relativistic regime. The simulations in which the wave is resonantly excited are compared to cases in which the resonant conditions are not provided and the coupling of the laser with the target is analyzed. We have considered the following aspects of the laser-plasma interaction, for different laser and target parameters: i) the laser absorption and the electric field at the surface ii) the generation of a quasi-static magnetic field iii) the electron heating and iiii) the ion acceleration. The possibility to excite a surface plasma wave on a structured target for a large range of laser energies has been demonstrated. In the cases where the surface wave is excited the electric field component normal to the target is amplified at the surface by a factor ranging from 3.2 to 7.2 with respect to the laser field. The absorption is also increased,for example it raises from 27% when the SPW is not excited up to 73% for Iλ^2=10^9 μm^2/Wcm^2. We have defined the optimal conditions for efficient coupling which increase laser absorption, that correspond to the relativistic laser intensities (Iλ^2>10^19 μm^2/Wcm^2). In this regime the main absorption mechanism is vacuum heating, associated to particles oscillating in the field perpendicular to the target, which is enhanced by the stronger, localized field of the SPW. The generation of a quasi-static magnetic field has been studied analytically and compared to the result of PIC simulations. The different field structure in presence of a SPW and for a flat target suggests that the enhanced field strength has caused partial confinement of particles at the target surface when SPW is present. The effects of the surface wave are more pronounced in thin laminar targets where electrons recirculate into the target interacting several times with the wave. Efficient electron heating increases the energy of the ions which are accelerated at both the irradiated and not irradiated target surface by the hot electrons space charge field. For the thinnest target (3.5 μm) the ion cut-off energy is about 14 Mev, approximately twice the value obtained when the SPW is not excited.
• Speeding up the solution of the Bethe-Salpeter equation by a double-grid method and Wannier interpolation
  
  • Kammerlander David
  • Botti Silvana
  • Marques Miguel A. L.
  • Marini Andrea
  • Attaccalite Claudio
  Physical Review B: Condensed Matter and Materials Physics (1998-2015), American Physical Society, 2012, 86 (12), pp.125203. The Bethe-Salpeter equation is a widely used approach to describe optical excitations in bulk semiconductors. It leads to spectra that are in very good agreement with experiment, but the price to pay for such accuracy is a very high computational burden. One of the main bottlenecks is the large number of k-points required to obtain converged spectra. In order to circumvent this problem we propose a strategy to solve the Bethe-Salpeter equation based on a double-grid technique coupled to a Wannier interpolation of the Kohn-Sham band structure. This strategy is then benchmarked for a particularly difficult case, the calculation of the absorption spectrum of GaAs, and for the well studied case of Si. The considerable gains observed in these cases fully validate our approach, and open the way for the application of the Bethe-Salpeter equation to large and complex systems. (10.1103/PhysRevB.86.125203)
  DOI : 10.1103/PhysRevB.86.125203
• Tailoring of SiC nanoprecipitates formed in Si
  
  • Velisa G.
  • Trocellier P.
  • Thome L.
  • Vaubaillon S.
  • Miro S.
  • Serruys Y.
  • Bordas E.
  • Meslin E.
  • Mylonas S.
  • Coulon P.E.
  • Lepretre F.
  • Pilz A.
  • Beck L.
  , 2013, 307, pp.165-170. The SiC synthesis through single-beam of C+, and simultaneous-dual-beam of C+ & Si+ ion implantations into a Si substrate heated at 550 degrees C has been studied by means of three complementary analytical techniques: nuclear reaction analysis (NRA), Raman, and transmission electron microscopy (TEM). It is shown that a broad distribution of SiC nanoprecipitates is directly formed after simultaneous-dual-beam (520-keV C+ & 890-keV Si+) and single-beam (520-keV C+) ion implantations. Their shape appear as spherical (average size similar to 4-5 nm) and they are in epitaxial relationship with the silicon matrix. (C) 2013 Elsevier B.V. All rights reserved. (10.1016/j.nimb.2012.12.089)
  DOI : 10.1016/j.nimb.2012.12.089
• Electron irradiation of Co, Ni, and P-doped BaFe2As2 - type iron-based superconductors
  
  • van Der Beek Cornelis Jacominus
  • Demirdis Sultan
  • Colson Dorothée
  • Rullier-Albenque F.
  • Fasano Yanina
  • Shibauchi Takasada
  • Matsuda Yuji
  • Kasahara Shigeru
  • Gierlowski Piotr
  • Konczykowski Marcin
  Journal of Physics: Conference Series, IOP Science, 2013, 449, pp.012023. High energy electron irradiation is used to controllably introduce atomic-scale point defects into single crystalline Ba(Fe_1-xCo_x)_2As_2, Ba(Fe_1-xNi_x)_2As_2, and BaFe_2(As_1-xP_x)_2. The appearance of the collective pinning contribution to the critical current density in BaFe_2(As_1-xP_x)_2, and the magnitude of its enhancement in Ba(Fe_1-xCo_x)_2As_2, conform with the hypothesis of quasi-particle scattering by Fe vacancies created by the irradiation. Whereas the insignificant modification of the temperature dependence of the superfluid density in Ba(Fe_1-xCo_x)_2As_2 and Ba(Fe_1-xNi_x)_2As_2 points to important native disorder present before the irradiation, the critical temperatures of these materials undergo a suppression equivalent to that observed in the much cleaner BaFe_2(As_1-xP_x)_2. This lends credence to the hypothesis of line nodes of the order parameter (at finite k_{z}) in the former two materials.
• Feedback mechanism for the stability of the band gap of CuInSe2
  
  • Gutay Levent
  • Regesch David
  • Larsen Jes K.
  • Aida Yasuhiro
  • Depredurand Valérie
  • Redinger Alex
  • Caneva Sabina
  • Schorr Susan
  • Stephan Christiane
  • Vidal Julien
  • Botti Silvana
  • Siebentritt Susanne
  Physical Review B: Condensed Matter and Materials Physics (1998-2015), American Physical Society, 2012, 86, pp.045216. (10.1103/PhysRevB.86.045216)
  DOI : 10.1103/PhysRevB.86.045216
• Anisotropy of strong pinning in multi-band superconductors
  
  • van Der Beek Cornelis Jacominus
  • Konczykowski Marcin
  • Prozorov Ruslan
  Superconductor Science and Technology, IOP Publishing, 2012, 25 (8), pp.084010. The field-angular dependence and anisotropy of the critical current density in iron-based superconductors is evaluated using a phenomenological approach featuring distinct anisotropy factors for the penetration depth and the coherence length. Both the weak collective pinning limit, and the strong pinning limit relevant for iron-based superconductors at low magnetic fields are considered. It is found that in the more anisotropic materials, such as SmFeAsO and NdFeAsO, the field-angular dependence is completely dominated by the coherence-length (upper-critical field) anisotropy, thereby explaining recent results on the critical current in these materials. In less anisotropic superconductors, strong pinning can lead to an apparent inversion of the anisotropy. Finally, it is shown that, under all circumstances, the ratio of c-axis and ab-plane critical current densities for magnetic field along the ab-plane directly yields the coherence length anisotropy factor εξ. (10.1088/0953-2048/25/8/084010)
  DOI : 10.1088/0953-2048/25/8/084010
• Large crystal local-field effects in second-harmonic generation of a Si/CaF2 interface: An ab initio study
  
  • Bertocchi Matteo
  • Luppi E.
  • Degoli E.
  • Véniard Valérie
  • Ossicini Stefano
  Physical Review B: Condensed Matter and Materials Physics (1998-2015), American Physical Society, 2012, pp.035309.
• Rational description of the ion-beam shaping mechanism
  
  • Rizza G.
  • Coulon P.
  • Khomenkov V.
  • Dufour C.
  • Monnet I.
  • Toulemonde M.
  • Perruchas S.
  • Gacoin T.
  • Mailly D.
  • Lafosse X.
  • Ulysse C.
  • Dawi E.
  Physical Review B, American Physical Society, 2012, 86 (3), pp.035450. (10.1103/PhysRevB.86.035450)
  DOI : 10.1103/PhysRevB.86.035450
• Vortex creep and critical current densities in superconducting (Ba,K)Fe_2As_2 single crystals
  
  • Konczykowski Marcin
  • van Der Beek Cornelis Jacominus
  • Tanatar Makariy A.
  • Luo Huiqian
  • Wang Zhaosheng
  • Shen Bing
  • Wen Haihu
  • Prozorov Ruslan
  Physical Review B: Condensed Matter and Materials Physics (1998-2015), American Physical Society, 2012, 86 (2), pp.024515. The surprisingly rapid relaxation of the sustainable current density in the critical state of single crystalline (Ba,K)Fe_2As_2 is investigated for magnetic fields oriented parallel to the c-axis and to the ab-plane respectively. Due to the inadequacy of standard analysis procedures developed for flux creep in the high temperature superconducting cuprates, we develop a simple, straightforward data treatment technique that reveals the creep mechanism and the creep exponent µ. At low magnetic fields, below the second magnetization peak, µ varies only slightly as function of temperature and magnetic flux density B. From the data, we determine the temperature- and field dependence of the effective activation barrier for creep. At low temperatures, the measured current density approaches the zero--temperature critical current density (in the absence of creep) to within a factor 2, thus lending credence to earlier conclusions drawn with respect to the pinning mechanism. The comparable values of the experimental screening current density and the zero-temperature critical current density reveals the limited usefulness of the widely used ''interpolation formula''. (10.1103/PhysRevB.86.024515)
  DOI : 10.1103/PhysRevB.86.024515