Superfluid transition temperature and fluctuation theory of spin-orbit and Rabi-coupled fermions with tunable interactions

TL;DR

This paper investigates how spin-orbit and Rabi couplings influence the superfluid transition temperature and phase transitions in fermionic systems across the BCS-BEC crossover, providing a comprehensive fluctuation theory.

Contribution

It introduces a detailed fluctuation theory and analyzes the effects of spin-orbit and Rabi couplings on phase transition order and critical temperature in fermionic superfluids.

Findings

Spin-orbit coupling enhances critical temperature in BEC limit.

Spin-orbit coupling can change phase transition from first to second order.

Derived a sixth-order Ginzburg-Landau free energy for superfluid transitions.

Abstract

We obtain the superfluid transition temperature of equal Rashba-Dresselhaus spin-orbit and Rabi-coupled Fermi superfluids, from the Bardeen-Cooper-Schrieffer (BCS) to Bose-Einstein condensate (BEC) regimes in three dimensions for tunable $s$-wave interactions. In the presence of Rabi coupling, we find that spin-orbit coupling enhances (reduces) the critical temperature in the BEC (BCS) limit. For fixed interactions, we show that spin-orbit coupling can convert a first-order (discontinuous) phase transition into a second-order (continuous) phase transition, as a function of Rabi coupling. We derive the Ginzburg-Landau free energy to sixth power in the superfluid order parameter to describe both continuous and discontinuous phase transitions as a function of spin-orbit and Rabi couplings. Lastly, we develop a time-dependent Ginzburg-Landau fluctuation theory for an arbitrary mixture of Rashba and Dresselhaus spin-orbit couplings at any interaction strength.