Impurity probe of topological superfluid in one-dimensional spin-orbit coupled atomic Fermi gases

TL;DR

This paper theoretically studies how non-magnetic impurities affect one-dimensional topological superfluids in ultracold atomic gases, revealing universal bound states that could serve as evidence of topological order.

Contribution

It predicts the formation of universal impurity-bound states in topological superfluids, distinct from trivial superfluids, providing a potential experimental signature of topological phases.

Findings

Universal zero-energy bound states near impurities in topological superfluids.

Bound states closely resemble Majorana fermions.

Potential experimental detection in ultracold $^{40}$K gases.

Abstract

We investigate theoretically non-magnetic impurity scattering in a one-dimensional atomic topological superfluid in harmonic traps, by solving self-consistently the microscopic Bogoliubov-de Gennes equation. In sharp contrast to topologically trivial Bardeen-Cooper-Schrieffer \textit{s}-wave superfluid, topological superfluid can host a mid-gap state that is bound to localized non-magnetic impurity. For strong impurity scattering, the bound state becomes universal, with nearly zero energy and a wave-function that closely follows the symmetry of that of Majorana fermions. We propose that the observation of such a universal bound state could be a useful evidence for characterizing the topolgoical nature of topological superfluids. Our prediction is applicable to an ultracold resonantly-interacting Fermi gas of $^{40}$K atoms with spin-orbit coupling confined in a two-dimensional optical lattice.