Universal impurity-induced bound state in topological superfluids

TL;DR

This paper predicts a universal impurity-induced bound state in topological superfluids, which can serve as a clear signature for identifying such phases, supported by theoretical calculations in ultracold atomic gases.

Contribution

It introduces the concept of a universal impurity-induced bound state in topological superfluids and proposes a realistic experimental scenario for observation.

Findings

Universal bound state exists in topological superfluids with impurities.

The bound state is similar to vortex core bound states but localized at impurities.

Proposed observation in ultracold $^{40}$K atomic gases.

Abstract

We predict a universal mid-gap bound state in topological superfluids, induced by either non-magnetic or magnetic impurities in the strong scattering limit. This universal state is similar to the lowest-energy Caroli-de Gennes-Martricon bound state in a vortex core, but is bound to localized impurities. We argue that the observation of such a universal bound state can be a clear signature for identifying topological superfluids. We theoretically examine our argument for a spin-orbit coupled ultracold atomic Fermi gas trapped in a two-dimensional harmonic potential, by performing extensive self-consistent calculations within the mean-field Bogoliubov-de Gennes theory. A realistic scenario for observing universal bound state in ultracold $^{40}$K atoms is proposed.