We report thermal transport properties of a ${\mathrm{K}}_x$Fe${}_{2-y}$Se${}_2$ superconducting single crystal. A peak anomaly in the thermal conductivity is observed at nearly $T_C/2$, attributed to phonons. The thermoelectric power above $T_c$ exhibits nearly linear behavior and could be described well by the carrier diffusion mechanism in a wide temperature range. The zero-temperature extrapolated thermoelectric power is smaller than the value in typical strongly correlated superconductors, implying a large normalized Fermi temperature. These findings indicate that ${\mathrm{K}}_x$Fe${}_{2-y}$Se${}_2$ is a weakly or intermediately correlated superconductor.

• Received 11 February 2011

DOI:https://doi.org/10.1103/PhysRevB.83.174503