Three-dimensional spin-orbit coupled Fermi gases: Fulde-Ferrell pairing, Majorana fermions, Weyl fermions and gapless topological superfluidity

TL;DR

This paper explores the rich phase diagram of a three-dimensional spin-orbit coupled Fermi gas under Zeeman fields, revealing inhomogeneous pairing, topological phases, and exotic quasiparticles like Weyl and Majorana fermions.

Contribution

It introduces a comprehensive theoretical analysis of topological superfluid phases, including Fulde-Ferrell pairing and Weyl fermions, in 3D spin-orbit coupled Fermi gases with Zeeman fields.

Findings

Identification of inhomogeneous Fulde-Ferrell pairing phases.

Discovery of topological superfluid phases with Weyl nodes.

Phase diagrams at zero and finite temperatures showing diverse phases.

Abstract

We theoretically investigate a three-dimensional Fermi gas with Rashba spin-orbit coupling in the presence of both out-of-plane and in-plane Zeeman fields. We show that, driven by a sufficiently large Zeeman field, either out-of-plane or in-plane, the superfluid phase of this system exhibits a number of interesting features, including inhomogeneous Fulde-Ferrell pairing, gapped or gapless topological order and exotic quasi-particle excitations known as Weyl fermions that have linear energy dispersions in momentum space (i.e., massless Dirac fermions). The topological superfluid phase can have either four or two topologically protected Weyl nodes. We present the phase diagrams at both zero and finite temperatures and discuss the possibility of their observation in an atomic Fermi gas with synthetic spin-orbit coupling. In this context, topological superfluid phases with an imperfect Rashba spin-orbit coupling are also studied.