Specific Heat to 35 T in P-doped and Co-doped BaFe$_{2}$As$_{2}$: Evidence for Nodes or Not?

ORAL

Abstract

We have measured the low temperature specific heat of annealed single crystal Ba(Fe$_{0.955}$Co$_{0.045})_{2}$As$_{2}$, unannealed single crystal BaFe$_{2}$(As$_{0.7}$P$_{0.3})_{2}$, and other BaFe$_{2}$As$_{2}$ derivatives in fields to 35 T. We report contrasting behavior, with the underdoped Co sample exhibiting behavior (specific heat $\gamma \quad \sim $ H$^{0.7})$ essentially up to H$_{c2}$ similar to the Volovik effect prediction ($\gamma \quad \sim $ H**0.5) for nodal behavior for fields H $<$ 0.1H$_{c2}$. In contrast, $\gamma $ up to 35 T (2/3 of H$_{c2})$ in BaFe$_{2}$(As$_{0.7}$P$_{0.3})_{2}$ exhibits linear with field dependence, consistent with fully gapped behavior but inconsistent with indications of nodal behavior from other measurements. Possible explanations, and up-to-date measurements will be presented.

*Work at Florida supported by DE-FG02-86ER45268 (GRS, JSK), DE-FG02-05ER46236 (PJH).

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Authors

  • G.R. Stewart

    • Physics, University of Florida

  • J.S. Kim

    • Physics, University of Florida

  • Peter Hirschfeld

    • Department of Physics, University of Florida, Gainesville, FL 32611, USA
    • Physics, University of Florida
    • University of Florida
    • Department of Physics, University of Florida, Gainesville, Florida 32611, USA

  • Filip Ronning

    • Los Alamos National Laboratory
    • MPA-10, Los Alamos National Laboratory
    • Los Alamos National Lab, MPA-CMMS
    • Los Alamos National Laboratory, Los Alamos, NM 87545

  • Krzysztof Gofryk

    • MPA-10, Los Alamos National Laboratory
    • Los Alamos National Laboratory

  • A.S. Sefat

    • ORNL
    • Oak Ridge National Laboratory, Oak Ridge, TN 37831, USA
    • Oak Ridge National Laboratory
    • MST Division, Oak Ridge National Laboratory
    • ORNL, Oak Ridge, TN
    • Oak Ridge National Laboratory (ORNL), Oak Ridge, TN 37831, USA
    • Materials Science \& Technology Division, ORNL, Oak Ridge, TN 37831, USA

  • S. Kasahara

    • Kyoto University
    • Physics, Kyoto University
    • Research Center for Low Temperature and Materials Sciences, Kyoto University, Sakyo-ku, Kyoto 606-8501, Japan
    • Department of Physics, Kyoto University, Kyoto 606-8502, Japan

  • T. Shibauchi

    • Physics, Kyoto University
    • Department of Physics, Kyoto University, Sakyo-ku, Kyoto 606-8502, Japan
    • Department of Physics, Kyoto University, Kyoto 606-8502, Japan

  • T. Terashima

    • Physics, Kyoto University

  • Yuji Matsuda

    • Physics, Kyoto University
    • Department of Physics, Kyoto University, Sakyo-ku, Kyoto 606-8502, Japan
    • Department of Physics, Kyoto University, Kyoto 606-8502, Japan