BCS-BEC crossover at finite temperature in spin-orbit coupled Fermi gases

TL;DR

This paper investigates how different types of spin-orbit coupling affect the superfluid transition and pseudogap formation in three-dimensional Fermi gases at finite temperature, revealing a BCS-BEC crossover influenced by SOC strength.

Contribution

It introduces a $T$-matrix-based method to analyze the effects of pairing fluctuations on SOC Fermi gases, identifying SOC-dependent BCS-BEC crossover and pseudogap phenomena.

Findings

Critical temperature signals BCS-BEC crossover for EO and S SOC types.

Strong SOC can induce sizable pseudogaps even at weak coupling.

At strong SOC, critical temperatures approach those of ideal rashbon BEC.

Abstract

By adopting a $T$-matrix-based method within the $G_0G$ approximation for the pair susceptibility, we study the effects of the pairing fluctuation on the three-dimensional spin-orbit coupled Fermi gases at finite temperature. The critical temperatures of the superfluid/normal phase transition are determined for three different types of spin-orbit coupling (SOC): (1) the extreme oblate (EO) or Rashba SOC, (2) the extreme prolate (EP) or equal Rashba-Dresselhaus SOC, and (3) the spherical (S) SOC. For EO- and S-type SOC, the SOC dependence of the critical temperature signals a crossover from BCS to BEC state; at strong SOC limit, the critical temperature recover those of ideal BEC of rashbons. The pairing fluctuation induces a pseudogap in the fermionic excitation spectrum in both superfluid and normal phases. We find that, for EO- and S-type SOC, even at weak coupling, sufficiently strong SOC can induce sizable pseudogap. Our research suggests that the spin-orbit coupled Fermi gases may open new means to the study of the pseudogap formation in fermionic systems.