Gapless Surfaces in Anisotropic Superfluids

TL;DR

This paper investigates the emergence of gapless surfaces in anisotropic superfluids with p-wave pairing between mismatched Fermi surfaces, analyzing their stability and physical properties.

Contribution

It provides detailed calculations and stability analysis of gapless superfluid states with broken rotation symmetry, proposing realizability in cold atom systems.

Findings

Gapless surfaces occur in p-wave paired superfluids with mismatched Fermi surfaces.

The breached superfluid state can be stable over a range of parameters.

Homogeneous models with spontaneous symmetry breaking are proposed as realizable in cold atom experiments.

Abstract

We demonstrate when p-wave pairing occurs between species whose free Fermi surfaces are mismatched the gap generally vanishes over a two-dimensional surface. We present detailed calculations of condensation energy, superfluid density (Meissner mass) and specific heat for such states. We also consider stability against separation into mixed phases. According to several independent criteria that can be checked at weak coupling, the resulting ``breached'' state appears to be stable over a substantial range of parameters. The simple models we consider are homogeneous in position space, and break rotation symmetry spontaneously. They should be realizable in cold atom systems.