Thermodynamic Determination of the Upper Critical Field and Anisotropy of Ba$_{0.6}$K$_{0.4}$Fe$_{2}$As$_{2}$ Single Crystals

ORAL

Abstract

We present anisotropic heat capacity measurements of the upper critical field of Ba$_{0.6}$K$_{0.4}$Fe$_{2}$As$_{2}$ single crystals in fields up to 8 Tesla. In zero-magnetic field a clear step in the heat capacity is observed at T$_{c} \sim $36K. Using an entropy conserving construction we determined the transition temperatures in applied fields and the upper critical field slopes dH$_{c2 \vert \vert c}$/dT = -6.5 T/K and dH$_{c2 \vert \vert ab}$/dT -17.4 T/K, the latter showing record high critical field slope near T$_{c}$. The temperature dependence of the specific heat of Ba$_{0.6}$K$_{0.4}$Fe$_{2}$As$_{2}$ indicates strong coupling effects. Based on the experimental values of the upper critical field slopes, we determined the Ginzburg parameter, coherence and penetration lengths, anisotropy and thermodynamic critical fields. We also present magnetization measurements and discuss their implications on the nature of critical currents in this material.

*This work was supported by the US Department of Energy, BES-Materials Sciences, under Contract DE-AC02-06CH11357.

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Authors

  • Wai -K. Kwok

    • Materials Science Division, Argonne National Laboratory, Argonne, IL 60439, USA
    • Argonne National Lab,*Northern Illinois University
    • Argonne National Laboratory
    • Argonne National Lab
    • Argonne National Laboratory, Argonne, IL 60439, USA

  • Ulrich Welp

    • Materials Science Division, Argonne National Laboratory, Argonne, IL 60439, USA
    • Argonne National Laboratory
    • Argonne National Laboratory, Argonne, IL 60439, USA

  • Ruobing Xie

    • Materials Science Division, Argonne National Laboratory, Argonne, IL 60439, USA

  • Alex Koshelev

    • Materials Science Division, Argonne National Laboratory, Argonne, IL 60439, USA
    • Materials Science Division, Argonne National Laboratory
    • Argonne National Laboratory, Argonne, IL 60439, USA
    • Argonne National Laboratory

  • J.A. Schlueter

    • Materials Science Division, Argonne National Laboratory, Argonne, IL 60439, USA
    • Argonne

  • Jiong Hua

    • Materials Science Division, Argonne National Laboratory, Argonne, IL 60439, USA

  • Hui-qian Luo

    • Institute of Physics, Chinese Academy of Sciences, Beijing, China

  • Zhao-sheng Wang

    • Institute of Physics, Chinese Academy of Sciences, Beijing, China

  • Gang Mu

    • Institute of Physics, Chinese Academy of Sciences, Beijing, China

  • Hai-Hu Wen

    • Institute of Physics, Chinese Academy of Sciences, Beijing, China
    • NLS CAS
    • National Laboratory for Superconductivity, Institute of Physics and Beijing National Laboratory for Condensed Matter Physics, CAS
    • IOP, CAS