Theory of thermal conductivity in extended-$s$ state superconductors: application to ferropnictides

摘要

Within a two-band model for the recently discovered ferropnictide materials,we calculate the thermal conductivity assuming general superconducting statesof $A_{1g}$ ("s-wave") symmetry, considering both currently popular isotropic"sign-changing" $s$ states and states with strong anisotropy, including thosewhich manifest nodes or deep minima of the order parameter. We consider bothintra- and interband disorder scattering effects, and show that in situationswhere a low-temperature linear-$T$ exists in the thermal conductivity, it isnot always "universal" as in d-wave superconductors. We discuss the conditionsunder which such a term can disappear, as well as how it can be induced by amagnetic field. We compare our results to several recent experiments.