BCS-BEC Crossover and Topological Phase Transition in 3D Spin-Orbit Coupled Degenerate Fermi Gases

TL;DR

This paper explores how spin-orbit coupling and Zeeman fields influence the BCS-BEC crossover and induce topological phase transitions in 3D degenerate Fermi gases, revealing new topological superfluid states with Weyl fermion excitations.

Contribution

It demonstrates that SOC can restore superfluidity under strong Zeeman fields and identifies a sequence of topological phase transitions with experimentally detectable signatures.

Findings

Superfluid order parameter is restored by SOC despite large Zeeman fields.

Sequence of topological phase transitions with changing Zeeman field.

Existence of Weyl fermion-like quasiparticles at Fermi points.

Abstract

We investigate the BCS-BEC crossover in three dimensional degenerate Fermi gases in the presence of spin-orbit coupling (SOC) and Zeeman field. We show that the superfluid order parameter destroyed by a large Zeeman field can be restored by the SOC. With increasing strengths of the Zeeman field, there is a series of topological quantum phase transitions from a non-topological superfluid state with fully gapped fermionic spectrum to a topological superfluid state with four topologically protected Fermi points (i.e., nodes in the quasiparticle excitation gap) and then to a second topological superfluid state with only two topologically protected Fermi points. The quasiparticle excitations near the Fermi points realize the long-sought low-temperature analog of Weyl fermions of particle physics. We show that the topological phase transitions can be probed using the experimentally realized momentum resolved photoemission spectroscopy.