Gap symmetry and structure of Fe-based superconductors

TL;DR

This paper reviews how the diverse gap structures in Fe-based superconductors can be explained by spin fluctuation theory and their electronic structures, emphasizing the role of sign-changing s-wave symmetry.

Contribution

It offers a unified understanding of the varying gap structures in Fe-based superconductors through theoretical predictions and experimental evidence.

Findings

Superconducting gaps vary across Fe-based superconductor families.

Spin fluctuation theory explains the nonuniversality of gap structures.

Sign-changing s-wave (s±) symmetry is likely responsible for pairing.

Abstract

The recently discovered Fe-pnictide and chalcogenide superconductors display low-temperature properties suggesting superconducting gap structures which appear to vary substantially from family to family, and even within families as a function of doping or pressure. We propose that this apparent nonuniversality can actually be understood by considering the predictions of spin fluctuation theory and accounting for the peculiar electronic structure of these systems, coupled with the likely 'sign-changing s-wave' (s\pm) symmetry. We review theoretical aspects, materials properties and experimental evidence relevant to this suggestion, and discuss which further measurements would be useful to settle these issues.