Trapped Fermi gases with Rashba spin-orbit coupling in two dimensions

TL;DR

This paper investigates how Rashba spin-orbit coupling influences the phases, currents, and excitations in harmonically trapped two-dimensional Fermi gases across the BCS-BEC crossover, revealing destabilization of certain superfluid phases and topological interface modes.

Contribution

It provides a detailed analysis of the effects of Rashba spin-orbit coupling on trapped Fermi gases, including phase stability, mass currents, and topological interface modes, using the Bogoliubov-de Gennes formalism.

Findings

Small spin-orbit coupling destabilizes FFLO and phase-separated states.

Spin-orbit coupling induces countercirculating mass currents and intrinsic angular momentum.

Interface modes connect quasiparticle spectra depending on topological phases.

Abstract

We use the Bogoliubov-de Gennes formalism to analyze harmonically trapped Fermi gases with Rashba-type spin-orbit coupling in two dimensions. We consider both population-balanced and -imbalanced Fermi gases throughout the BCS-BEC evolution, and study the effects of spin-orbit coupling on the spontaneously induced countercirculating mass currents and the associated intrinsic angular momentum. In particular, we find that even a small spin-orbit coupling destabilizes Fulde-Ferrel-Larkin-Ovchinnikov (FFLO)-type spatially modulated superfluid phases as well as the phase-separated states against the polarized superfluid phase. We also show that the continuum of quasiparticle and quasihole excitation spectrum can be connected by zero, one or two discrete branches of interface modes, depending on the number of interfaces between a topologically trivial phase (e.g. locally unpolarized/low-polarized superfluid or spin-polarized normal) and a topologically nontrivial one (e.g. locally high-polarized superfluid) that may be present in a trapped system.