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Specific heat of Ca0.32Na0.68Fe2As2 single crystals: Unconventional s+/- multiband superconductivity with intermediate repulsive interband coupling and sizable attractive intraband couplings

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Rosner,  H.
Helge Rosner, Physics of Correlated Matter, Max Planck Institute for Chemical Physics of Solids, Max Planck Society;

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Citation

Johnston, S., Abdel-Hafiez, M., Harnagea, L., Grinenko, V., Bombor, D., Krupskaya, Y., et al. (2014). Specific heat of Ca0.32Na0.68Fe2As2 single crystals: Unconventional s+/- multiband superconductivity with intermediate repulsive interband coupling and sizable attractive intraband couplings. Physical Review B, 89(13): 134507, pp. 1-11. doi:10.1103/PhysRevB.89.134507.


Cite as: http://hdl.handle.net/11858/00-001M-0000-0019-DB25-8
Abstract
We report a low-temperature specific heat study of high-quality single crystals of the heavily hole-doped superconductor Ca0.32Na0.68Fe2As2. This compound exhibits bulk superconductivity with a transition temperature T-c approximate to 34 K, which is evident from the magnetization, transport, and specific heat measurements. The zero-field data manifest a significant electronic specific heat in the normal state with a Sommerfeld coefficient gamma approximate to 53 mJ/mol K-2. Using a multiband Eliashberg analysis, we demonstrate that the dependence of the zero-field specific heat in the superconducting state is well described by a three-band model with an unconventional s(+/-) pairing symmetry and gap magnitudes Delta(i) of approximately 2.35, 7.48, and -7.50 meV. Our analysis indicates a non-negligible attractive intraband coupling, which contributes significantly to the relatively high value of T-c. The Fermi surface averaged repulsive and attractive coupling strengths are of comparable size and outside the strong coupling limit frequently adopted for describing high-T-c iron pnictide superconductors. We further infer a total mass renormalization of the order of five, including the effects of correlations and electron-boson interactions.