## Superconducting gap with sign reversal between hole pockets in heavily hole-doped Ba1-xKxFe2As2    [PDF]

D. Watanabe, T. Yamashita, Y. Kawamoto, S. Kurata, Y. Mizukami, T. Ohta, S. Kasahara, M. Yamashita, T. Saito, H. Fukazawa, Y. Kohori, S. Ishida, K. Kihou, C. H. Lee, A. Iyo, H. Eisaki, A. B. Vorontsov, T. Shibauchi, Y. Matsuda
To gain insight into the unconventional superconductivity of Fe-pnictides with no electron pockets, we measure the thermal conductivity $\kappa$ and penetration depth $\lambda$ in the heavily hole-doped regime of Ba$_{1-x}$K$_x$Fe$_2$As$_2$. The residual thermal conductivity $(\kappa/T)_{T \rightarrow 0\,{\rm K}}$ and $T$-dependence of $\lambda$ consistently indicate the fully gapped superconductivity at $x=0.76$ and the (line) nodal superconductivity at higher hole concentrations. The magnitudes of $\frac{\kappa}{T}\cdot T_c|_{T \rightarrow 0\,{\rm K}}$ and $\frac{d\lambda}{d(T/T_c)}$ at low temperatures, both of which are determined by the properties of the low-energy excitations, exhibit a highly unusual non-monotonic x-dependence. These results indicate a dramatic change of the nodal characteristics in a narrow doping range, suggesting a doping crossover of the gap function between the s-wave states with and without sign reversal between $\Gamma$-centered hole pockets.
View original: http://arxiv.org/abs/1307.3408