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

TL;DR

This paper models thermal conductivity in ferropnictide superconductors with extended-s wave states, analyzing effects of disorder and anisotropy, and compares theoretical predictions with experimental data.

Contribution

It provides a detailed two-band model analysis of thermal conductivity in ferropnictides, including anisotropic states and disorder effects, extending understanding beyond isotropic s-wave assumptions.

Findings

Low-temperature linear-T thermal conductivity is not always universal.

Conditions for the disappearance or induction of linear-T term are identified.

Results align with several recent experimental observations.

Abstract

Within a two-band model for the recently discovered ferropnictide materials, we calculate the thermal conductivity assuming general superconducting states of $A_{1g}$ ("s-wave") symmetry, considering both currently popular isotropic "sign-changing" $s$ states and states with strong anisotropy, including those which manifest nodes or deep minima of the order parameter. We consider both intra- and interband disorder scattering effects, and show that in situations where a low-temperature linear-$T$ exists in the thermal conductivity, it is not always "universal" as in d-wave superconductors. We discuss the conditions under which such a term can disappear, as well as how it can be induced by a magnetic field. We compare our results to several recent experiments.