Abstract
We report low-temperature specific heat measurements for high-quality single crystalline KFeAs ( K). The investigated zero-field specific heat data yields an unusually large nominal Sommerfeld coefficient, mJ/mol K, which is, however, affected by extrinsic contributions as evidenced by a sizable residual linear specific heat and various theoretical considerations, including an analysis of Kadowaki-Woods relations. These results indicate that KFeAs should be classified as a weakly or intermediately coupled superconductor with a total electron-boson coupling constant (including a calculated weak electron-phonon coupling From specific heat and ac susceptibility studies in external magnetic fields the magnetic phase diagram is also constructed. We confirm the high anisotropy of the upper critical fields , ranging from a factor of 5 near to a slightly reduced value around 4.5 approaching for fields and and show that their ratio slightly exceeds the mean mass anisotropy of 4.4 derived from our full-relativistic local-density-approximation band structure calculations, also in accord with recent preliminary penetration depth data by Eskildsen et al. [Eskildsen, Forgan, and Kawano-Furukawa, Rep. Prog. Phys. 74, 124504 (2011)] near 4. Its slight reduction when approaching is not a consequence of Pauli limiting as in less perfect samples but points likely to a multiband effect. We also report irreversibility field data obtained from ac susceptibility measurements. The double-maximum in the dependence of its imaginary part for fields indicates a peak effect in the dependence of critical currents.
1 More- Received 28 October 2011
- Corrected 4 May 2012
DOI:https://doi.org/10.1103/PhysRevB.85.134533
©2012 American Physical Society
Corrections
4 May 2012