Magnetic Field Dependence of Specific Heat in KFe2As2 Single Crystals

Abstract

The observed change in specific heat by the application of a magnetic field for high-quality superconducting KFe2As2 single crystals by Abdel-Hafiez et al. (Phys. Rev. B 85, 134533–134543 (2012)) is examined through the phenomenological Ginzburg–Landau (GL) theory of anisotropic type II superconductors. In doing so, it is proposed that the system contains two gaps along two perpendicular directions, i.e., parallel to the ab plane and parallel to the c-axis as per the prediction through an angle-resolved photoemission spectroscopy (ARPES) experiment by Terashima et al. (J. Phys. Soc. Jpn. 78(8), 083701–083704 (2009)) and a de Haas-van Alphen (dHvA) experiment by Sato et al (Phys. Rev. Lett. 103, 047002–047006 (2009)). The single equation for the change of specific heat (ΔC) derived from the GL theory used to study the anisotropic property of cuprate superconductors by Pattanaik et al. (Physica B 405, 3234–3238 (2010)) is now approximately splitted into two equations along these perpendicular directions. The analysis of this equation explains satisfactorily the specific heat anomaly near T c and determines the penetration depth anisotropic ratio γ as 4.98, which is close to the experimental value 5.0 near T c by Abdel-Hafiez et al. (Phys. Rev. B 85, 134533–134543 (2012)) and the calculated value 4.0 by Eskildsen et al. (Rep. Prog. Phys. 74, 124504–1245016 (2011)).