Topological superfluid phases of an atomic Fermi gas with in- and out-of-plane Zeeman fields and equal Rashba-Dresselhaus spin-orbit coupling

TL;DR

This paper explores how in- and out-of-plane Zeeman fields combined with Rashba-Dresselhaus spin-orbit coupling induce novel topological and gapless superfluid phases in an atomic Fermi gas, revealing complex phase transitions and rich phase diagrams.

Contribution

It introduces a detailed analysis of topological superfluid phases and phase transitions in a Fermi gas with combined Zeeman fields and spin-orbit coupling, including the possibility of FFLO-like phases.

Findings

Identification of various topologically distinct gapless superfluid phases.

Observation of quantum phase transitions characterized by changes in Fermi surface topology.

Prediction of a rich phase diagram including uniform and nonuniform superfluid phases.

Abstract

We analyze the effects of in- and out-of-plane Zeeman fields on the BCS-BEC evolution of a Fermi gas with equal Rashba-Dresselhaus (ERD) spin-orbit coupling (SOC). We show that the ground state of the system involves novel gapless superfluid phases that can be distinguished with respect to the topology of the momentum-space regions with zero excitation energy. For the BCS-like uniform superfluid phases with zero center-of-mass momentum, the zeros may correspond to one or two doubly-degenerate spheres, two or four spheres, two or four concave spheroids, or one or two doubly-degenerate circles, depending on the combination of Zeeman fields and SOC. Such changes in the topology signal a quantum phase transition between distinct superfluid phases, and leave their signatures on some thermodynamic quantities. We also analyze the possibility of Fulde-Ferrell-Larkin-Ovchinnikov (FFLO)-like nonuniform superfluid phases with finite center-of-mass momentum and obtain an even richer phase diagram.