Transport properties of 3D extended s-wave states in Fe-based superconductors

TL;DR

This paper investigates the transport properties of extended-s wave superconducting states in Fe-based superconductors, explaining recent experimental results through theoretical modeling of superfluid density and thermal conductivity.

Contribution

It introduces a theoretical framework for understanding c-axis transport in Fe-pnictide superconductors with extended-s wave pairing, accounting for disorder and Fermi surface variations.

Findings

Recent experiments on Ba(Fe$_{1-x}$Co$_x$)$_2$As$_2$ are explained by the model.

The theory accounts for comparable c-axis and ab-plane transport coefficients.

Implications for the nature of the superconducting gap and Fermi surface are discussed.

Abstract

The Fermi surfaces of Fe-pnictide superconductors are fairly two-dimensional (2D), and it has thus come as a surprise that recent penetration depth and thermal conductivity measurements on systems of the 122 type have reported c-axis transport coefficients at low temperatures in the superconducting state comparable to or even larger than that in the $ab$-plane. These results should provide important information on both the Fermi surface and the superconducting state. Here we consider the theory of the superfluid density and thermal conductivity in models of extended-$s$ wave superconducting states expected to be appropriate for Fe-pnictide systems. We include intraband disorder and consider a range of different Fermi surfaces where gap nodes might exist. We show that recent experiments on Ba(Fe$_{1-x}$Co$_x$)$_2$As$_2$ can be semiquantitatively understood by such an approach, and discuss their implications.