The Fulde-Ferrell-Larkin-Ovchinnikov state in pnictides

TL;DR

This paper investigates the potential for FFLO superconducting states in Fe-based superconductors, demonstrating their support for such states regardless of order parameter symmetry and identifying conditions where a nonzero momentum state is the ground state.

Contribution

It provides the first analysis of FFLO phase support in two-band FeSC, showing its existence across different order parameter symmetries and identifying parameter ranges for nonzero momentum ground states.

Findings

FeSC can support FFLO phases regardless of order parameter symmetry

Nonzero Cooper pair momentum state can be the ground state under certain conditions

Supports the existence of oscillating order parameter in Fe-based superconductors

Abstract

Fe-based superconductors (FeSC) exhibit all the properties of systems that allow the formation of a superconducting phase with oscillating order parameter, called the Fulde--Ferrell--Larkin--Ovchinnikov (FFLO) phase. By the analysis of the Cooper pair susceptibility in two-band FeSC, such systems are shown to support the existence of a FFLO phase, regardless of the exhibited order parameter symmetry. We also show the state with nonzero Cooper pair momentum, in superconducting FeSC with $\sim \cos(k_{x}) \cdot \cos (k_{y})$ symmetry, to be the ground state of the system in a certain parameter range.