Specific Heat of Ba_0.59K_0.41Fe₂As₂, an Fe-Pnictide Superconductor with T_c = 36.9 K, and a New Method for Identifying the Electron Contribution [Specific Heat of Ba_0.59K_0.41Fe₂As₂, and a New Method for Identifying the Electron Contribution: Two Electron Bands with Different Energy Gaps in the Superconducting State]

Journal Article · 30 September 2015 · Journal of the Physical Society of Japan

DOI: https://doi.org/10.7566/JPSJ.84.114701 · OSTI ID:1466691

Rotundu, Costel R. ^[1]; Forrest, Thomas R. ^[2]; Phillips, Norman E. ^[3]; Birgeneau, Robert J. ^[3]

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1. Lawrence Berkeley National Lab. (LBNL), Berkeley, CA (United States); UCLA, Los Angeles, CA (United States)
2. Univ. of California, Berkeley, CA (United States); European Synchrotron Radiation Facility, Grenoble Cedex (France)
3. Lawrence Berkeley National Lab. (LBNL), Berkeley, CA (United States); Univ. of California, Berkeley, CA (United States)

Here, we report specific-heat measurements on Ba_0.59K_0.41Fe₂As₂, one of a family of high-T_cFe-pnictide superconductors for which the pairing interaction is of special interest. We use a new method, based on direct comparisons of α-model expressions for the electron contribution with the measured total specific heat, to extract the electron contribution. It circumvents the need in the conventional analyses for an independent, necessarily approximate, determination of the lattice contribution, which is subtracted from the total to obtain the electron contribution, and it eliminates the consequent uncertainties in the electron contribution. For Ba_0.59K_0.41Fe₂As₂ the electron density of states is comprised of contributions from two electron bands with superconducting-state energy gaps differing by a factor 3.8, with 77% coming from the band with the larger gap. The vortex-state specific heat suggests nodeless gaps. Comparison of the normal-state density of states with band-structure calculations shows an extraordinarily large effective mass enhancement, for which there is no precedent in simple metals and no theoretical explanation.

• Research Organization: Lawrence Berkeley National Laboratory (LBNL), Berkeley, CA (United States)
• Sponsoring Organization: USDOE Office of Science (SC), Basic Energy Sciences (BES) (SC-22)
• Grant/Contract Number: AC02-05CH11231
• OSTI ID: 1466691
• Journal Information: Journal of the Physical Society of Japan, Journal Name: Journal of the Physical Society of Japan Journal Issue: 11 Vol. 84; ISSN 0031-9015
• Publisher: Physical Society of JapanCopyright Statement
• Country of Publication: United States
• Language: English