Unconventional sign-reversing superconductivity in LaFeAsO_(1-x)F_x

TL;DR

This paper proposes that superconductivity in LaFeAsO_(1-x)F_x is unconventional, mediated by antiferromagnetic spin fluctuations, with an extended s-wave pairing state featuring a sign reversal of the order parameter.

Contribution

It introduces a novel mechanism for superconductivity in Fe-based compounds involving sign-reversing extended s-wave pairing driven by magnetic fluctuations.

Findings

Superconductivity is mediated by antiferromagnetic spin fluctuations.

The pairing state is an extended s-wave with sign reversal.

Doping suppresses ferromagnetic fluctuations, facilitating superconductivity.

Abstract

We argue that the newly discovered superconductivity in a nearly magnetic, Fe-based layered compound is unconventional and mediated by antiferromagnetic spin fluctuations, though different from the usual superexchange and specific to this compound. This resulting state is an example of extended s-wave pairing with a sign reversal of the order parameter between different Fermi surface sheets. The main role of doping in this scenario is to lower the density of states and suppress the pair-breaking ferromagnetic fluctuations.