Topological Fulde-Ferrell Superfluids of a Spin-Orbit Coupled Fermi Gas

TL;DR

This paper explores topological Fulde-Ferrell superfluids in spin-orbit coupled Fermi gases, revealing their phase diagrams, exotic quasiparticles like Majorana and Weyl fermions, and potential experimental detection methods.

Contribution

It introduces the concept of topological Fulde-Ferrell superfluids in spin-orbit coupled Fermi gases, analyzing their phase diagrams and quasiparticle properties in various dimensions.

Findings

Fulde-Ferrell states are enhanced by spin-orbit coupling and Zeeman fields.

Topological phases host Majorana and Weyl fermions with unique dispersion.

Proposed methods for experimental detection in cold atom systems.

Abstract

Topological Fermi superfluids have played the central role in various fields of physics. However, all previous studies focus on the cases where Cooper pairs have zero center-of-mass momenta (i.e. normal superfluids). The topology of Fulde-Ferrell superfluids with nonzero momentum pairings have never been explored until recent findings that Fulde-Ferrell superfluids in a spin-orbit coupled Fermi gas can accommodate Majorana fermions in real space in low dimensions and Weyl fermions in momentum space in three dimension. In this review, we first discuss the mechanism of pairings in spin-orbit coupled Fermi gases in optical lattices subject to Zeeman fields, showing that spin-orbit coupling as well as Zeeman fields enhance Fulde-Ferrell states while suppress Larkin-Ovchinnikov states. We then present the low temperature phase diagram including both FF superfluids and topological FF superfluids phases in both two dimension and three dimension. In one dimension, Majorana fermions as well as phase dependent order parameter are visualized. In three dimension, we show the properties of Weyl fermions in momentum space such as anisotropic linear dispersion, Fermi arch, and gaplessness away from $k_{\perp}=0$. Finally, we discuss some possible methods to probe FF superfluids and topological FF superfluids in cold atom systems.