Broken translational and time-reversal symmetry in superconducting films

TL;DR

This paper reveals that thin films of d-wave superconductors can develop novel phases at low temperatures, breaking translational or time-reversal symmetry due to inhomogeneities, similar to FFLO states.

Contribution

It introduces the possibility of new symmetry-breaking superconducting phases in thin films caused by transverse inhomogeneity.

Findings

Superconducting films can exhibit periodic order parameter structures.

Superconducting films can develop supercurrents along the film.

New phases emerge below 0.43 T_c due to inhomogeneity.

Abstract

We demonstrate that films of unconventional (d-wave) superconductor at temperatures $T\lesssim 0.43 T_c$ can exhibit unusual superconducting phases. The new ground states beside the broken gauge and the point group symmetries can spontaneously break (i) continuous translational symmetry and form periodic order parameter structures in the plane of the film, or (ii) time-reversal symmetry and develop supercurrent flowing along the film. These states are result of the strong transverse inhomogeniety present in films with thickness of several coherence lengths. We show a natural similarity between formation of these states and the Fulde-Ferrell-Larkin-Ovchinnikov state.