FFLO state in thin superconducting films

TL;DR

This paper analyzes the FFLO superconducting state in thin films under parallel magnetic fields, predicting unique in-plane angular dependencies of critical fields and currents that could serve as clear indicators of FFLO phase formation.

Contribution

It provides the first detailed prediction of angular dependence of critical fields and critical currents in FFLO states in thin superconducting films with tetragonal symmetry.

Findings

In-plane critical field shows peculiar angular dependence due to orbital effects.

Strong critical current anisotropy is predicted in the FFLO state.

Critical field remains isotropic in the uniform superconducting state.

Abstract

We present the analysis of the inhomogeneous Fulde-Ferrell-Larkin-Ovchinnikov (FFLO) superconducting state in thin superconducting films in the parallel magnetic field. For the tetragonal crystal symmetry (relevant to CeCoIn$_{5}$ - the most probable candidate for the FFLO state formation) we predict a very peculiar in-plane angular dependence of the FFLO critical field due to the orbital effect. In the uniform superconducting state the critical field should be isotropic. The magnetic field pins also the direction of the FFLO modulation permitting thus to study the critical current anisotropy. Our calculations reveal a strong critical current anisotropy in the FFLO state in sharp contrast with the usual superconducting state. The predicted characteristic anisotropies of the critical field and critical current may provide an unambiguous probe of the FFLO phase formation.