Spin-orbit-coupled topological Fulde-Ferrell states of fermions in a harmonic trap

TL;DR

This paper explores the emergence of topological Fulde-Ferrell states with Majorana modes in spin-orbit-coupled ultracold Fermi gases confined in a trap, revealing new quantum phases and their experimental signatures.

Contribution

It provides a systematic theoretical analysis of topological Fulde-Ferrell states in spin-orbit-coupled Fermi gases, including analytical wavefunctions of Majorana modes and their dynamical behavior.

Findings

Topological Fulde-Ferrell states with Majorana modes are predicted.

Analytical wavefunctions for Majorana excitations are derived.

Expansion dynamics reveal signatures of finite-momentum pairing.

Abstract

Motivated by recent experimental breakthroughs in generating spin-orbit coupling in ultracold Fermi gases using Raman laser beams, we present a systematic study of spin-orbit-coupled Fermi gases confined in a quasi-one-dimensional trap in the presence of an in-plane Zeeman field (which can be realized using a finite two-photon Raman detuning). We find that a topological Fulde-Ferrell state will emerge, featuring finite-momentum Cooper pairing and zero-energy Majorana excitations localized near the edge of the trap based on the self-consistent Bogoliubov-de Genes (BdG) equations. We find analytically the wavefunctions of the Majorana modes. Finally using the time-dependent BdG we show how the finite-momentum pairing field manifests itself in the expansion dynamics of the atomic cloud.