Temperature Dependent Anisotropy of Oxypnictide Superconductors Studied by Torque Magnetometry

ORAL

Abstract

Single crystals of different oxypnictide superconductors of the family ReFeAsO$_{1-x}$F$_{y}$ (Re $=$ Sm, Nd, Pr) with various carrier dopings and with masses $m\simeq100$ ng have been investigated by means of torque magnetometry. We present most recent data, obtained by using highly sensitive piezoresistive torque sensors from which the superconducting anisotropy parameter $\gamma$ and the in-plane magnetic penetration depth $\lambda_{ab}$ were extracted. As an important result $\gamma$ was found to increase strongly as the temperature is decreased from $T_c$ down to low temperatures. This unconventional temperature dependence of $\gamma$ is similar to that observed in the two-band superconductor MgB$_2$ and cannot be explained within the classical Ginzburg-Landau model. This scenario strongly suggests a new multi-band mechanism in the novel class of oxypnictide high-temperature superconductors.

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Authors

  • Stephen Weyeneth

    • Physics Institute, University of Zurich, 8057 Zurich, Switzerland

  • Roman Puzniak

    • Institute of Physics, Polish Academy of Sciences, 02-668 Warsaw, Poland

  • Nikolai D. Zhigadlo

    • Laboratory for Solid State Physics, ETH Zurich, 8093 Zurich, Switzerland

  • Sergiy Katrych

    • Laboratory for Solid State Physics, ETH Zurich, 8093 Zurich, Switzerland

  • Zbigniew Bukowski

    • Laboratory for Solid State Physics, ETH Zurich, 8093 Zurich, Switzerland

  • Janusz Karpinski

    • Laboratory for Solid State Physics, ETH Zurich, 8093 Zurich, Switzerland

  • Urs Mosele

    • Physics Institute, University of Zurich, 8057 Zurich, Switzerland

  • Stefan Kohout

    • Physics Institute, University of Zurich, 8057 Zurich, Switzerland

  • Josef Roos

    • Physics Institute, University of Zurich, 8057 Zurich, Switzerland

  • Hugo Keller

    • Physics Institute, University of Zurich, 8057 Zurich, Switzerland