Fully Gapped Superconducting State Based on a High Normal State Quasiparticle Density of States in Ba${}_{0.6}$K${}_{0.4}$Fe${}_2$As${}_2$ Single Crystals

Abstract

We report the specific heat (SH) measurements on single crystals of hole doped $FeAs$-based superconductor $B{a}_{0.6}{K}_{0.4}F{e}_{2}A{s}_2$. It is found that the electronic SH coefficient ${\hat{I}}_e^3(T)$ is not temperature dependent and increases almost linearly with the magnetic field in low temperature region. These point to a fully gapped superconducting state. Surprisingly the sharp SH anomaly $\hat{I}”C/T{|}_{T_c}$ reaches a value of 98 $mJ/mol{K}^2$ suggesting a very high normal state quasiparticle density of states (${\hat{I}}_n^3\approx 63mJ/mol{K}^2$). A detailed analysis reveals that the ${\hat{I}}_e^3(T)$ cannot be fitted with a single gap of s-wave symmetry due to the presence of a hump in the middle temperature region. However, our data indicate that the dominant part of the superconducting condensate is induced by an s-wave gap with the magnitude of about 6 meV.

5 pages, 5 figures