Showing papers in "Physical Review in 2012"

Feedback mechanism for the stability of the band gap of CuInSe2

Abstract: Feedback mechanism for the stability of the band gap of CuInSe2 Levent Gütay,1,* David Regesch,1 Jes K. Larsen,1,† Yasuhiro Aida,1,‡ Valérie Depredurand,1 Alex Redinger,1 Sabina Caneva,1 Susan Schorr,2 Christiane Stephan,2 Julien Vidal,3 Silvana Botti,4,5 and Susanne Siebentritt1 1Laboratory for Photovoltaics, University of Luxembourg, Belvaux, Luxembourg 2Helmholtz Center Berlin for Materials and Energy, Department Crystallography, Berlin, Germany 3King’s College London, Physics Department, WC2R 2LS London, United Kingdom 4Laboratoire des Solides Irradiés and ETSF, École Polytechnique, CNRS, CEA-DSM, 91128 Palaiseau, France 5Université de Lyon, F-69000 Lyon, France and LPMCN, CNRS, UMR 5586, Université Lyon 1, F-69622 Villeurbanne, France (Received 23 September 2011; revised manuscript received 5 June 2012; published 27 July 2012)

Magnetic penetration-depth measurements of a suppressed superfluid density of superconducting Ca0.5Na0.5Fe2As2 single crystals by proton irradiation

Abstract: We report on the dramatic effect of random point defects, produced by proton irradiation, on the superfluid density rho(s) in superconducting Ca0.5Na0.5Fe2As2 single crystals. The magnitude of the suppression is inferred from measurements of the temperature-dependent magnetic penetration depth lambda(T) using magnetic force microscopy. Our findings indicate that a radiation dose of 2 x 10(16) cm(-2) produced by 3 MeV protons results in a reduction of the superconducting critical temperature T-c by approximately 10%. In contrast, rho(s)(0) is suppressed by approximately 60%. This breakdown of the Abrikosov-Gorkov theory may be explained by the so-called "Swiss cheese model," which accounts for the spatial suppression of the order parameter near point defects similar to holes in Swiss cheese. Both the slope of the upper critical field and the penetration depth lambda(T/T-c)/lambda(0) exhibit similar temperature dependences before and after irradiation. This may be due to a combination of the highly disordered nature of Ca0.5Na0.5Fe2As2 with large intraband and simultaneous interband scattering as well as the s(+/-)-wave nature of short coherence length superconductivity.

Free-Free Transitions of the e-H System Inside a Dense Plasma Irradiated by a Laser Field at Very Low Incident-Electron Energies

Abstract: The free-free transition is studied for an electron-hydrogen atom in ground state when a low-energy electron (external) is injected into hydrogenic plasma in the presence of an external homogenous, monochromatic, and linearly polarized laser field. The effect of plasma screening is considered in the Debye-Huckel approximation. The calculations are performed in the soft photon limit. The incident electron is considered to be dressed by the laser field in a nonperturbative manner by choosing the Volkov solutions in both the initial and final channels. The space part of the scattering wave function for the electron is solved numerically by taking into account the electron exchange. The laser-assisted differential and total cross sections are calculated for single-photon absorption or emission and no-photon exchange in the soft photon limit, the laser intensity being much less than the atomic field intensity. The calculations have been carried out for various values of Debye parameter, ranging from 0.005 to 0.12. A strong suppression is noted in the laser-assisted cross sections as compared to the field-free situation. A significant difference is noted for the singlet and triplet cross sections. The suppression is much more in the triplet states.

Coulomb-driven cluster-glass behavior in Mn-intercalated Ti1+yS2

Abstract: We have investigated the low-temperature spin-glasslike phase in the intercalated transition-metal dichalcogenide Mn0.09Ti1.1S2. A departure from Curie–Weiss behavior in the paramagnetic regime indicated the formation of small ferromagnetically correlated clusters. The Vogel–Fulcher law provided an excellent description of relaxation times in the vicinity of the transition, showing that the glasslike phase occurs due to interaction between the clusters. Cole–Cole plots for data close to the transition were linear, which is consistent with a simple exponential distribution of cluster sizes. A Monte Carlo simulation of the dichalcogenide system, including excess self-intercalated Ti ions, gave an exponential cluster-size distribution for a relatively narrow range of concentration values of Mn and Ti ions, values that were consistent with those of the Mn0.09Ti1.1S2 sample. Strong commonality in the relaxation behavior with certain ferroelectric relaxor systems suggests underlying similarity in the microscopic structure of the clusters in both systems, which may be chainlike or quasi-one-dimensional.