Negative superfluid densities in superconducting films in a parallel magnetic field

TL;DR

This paper develops a theory explaining how disordered superconducting films in a parallel magnetic field can exhibit random superfluid densities, leading to spontaneous supercurrents and a phase transition to a spin-glass-like state.

Contribution

It introduces a novel theoretical framework for mesoscopic fluctuations causing negative superfluid densities in disordered superconducting films under magnetic fields.

Findings

Superfluid density becomes random in sign at strong magnetic fields.

Spontaneous supercurrents emerge in the ground state.

The system belongs to the universality class of the 2D XY spin glass.

Abstract

In this paper we develop a theory of mesoscopic fluctuations in disordered thin superconducting films in a parallel magnetic field. At zero temperature and sufficiently strong magnetic field the system undergoes a phase transition into a state characterized by a superfluid density, which is random in sign. Consequently, in this region, random supercurrents are spontaneously created in the ground state of the system, and it belongs to the same universality class as the two dimensional XY spin glass with a random sign of the exchange interaction.