Experimental observation of a topological band gap opening in ultracold Fermi gases with two-dimensional spin-orbit coupling

TL;DR

This paper reports the experimental realization of a two-dimensional spin-orbit coupling and a perpendicular Zeeman field in ultracold Fermi gases, leading to a topological band gap opening at the Dirac point, enabling exploration of topological quantum states.

Contribution

It introduces a simple scheme to generate 2D SOC and Zeeman field simultaneously in ultracold atoms, and experimentally observes the resulting topological band gap.

Findings

Successful generation of 2D SOC and Zeeman field in ultracold Fermi gases.

Observation of band gap opening at the Dirac point via radio-frequency spectroscopy.

Potential for exploring topological superfluids and exotic fermionic excitations.

Abstract

The recent experimental realization of synthetic spin-orbit coupling (SOC) opens a new avenue for exploring novel quantum states with ultracold atoms. However, in experiments for generating two-dimensional SOC (e.g., Rashba type), a perpendicular Zeeman field, which opens a band gap at the Dirac point and induces many topological phenomena, is still lacking. Here we theoretically propose and experimentally realize a simple scheme for generating two-dimension SOC and a perpendicular Zeeman field simultaneously in ultracold Fermi gases by tuning the polarization of three Raman lasers that couple three hyperfine ground states of atoms. The resulting band gap opening at the Dirac point is probed using spin injection radio-frequency spectroscopy. Our observation may pave the way for exploring topological transport and topological superfluids with exotic Majorana and Weyl fermion excitations in ultracold atoms.