BCS pairing state of a Dilute Bose Gas with Spin-Orbit Coupling

TL;DR

This paper investigates a two-component Bose gas with spin-orbit coupling, revealing that BCS pairing can occur with weak interactions and is favored over BEC at low densities, with a transition at higher densities.

Contribution

It demonstrates the formation of a BCS pairing state in a dilute Bose gas with spin-orbit coupling, a novel phase not previously characterized.

Findings

Bound states form for any scattering length due to spin-orbit coupling.

BCS pairing state is energetically favored over BEC at low densities.

First-order transition from BCS to BEC with increasing density.

Abstract

We study a two-component Bose gas with a symmetric spin-orbit coupling, and find that two atoms can form a bound state with any intra- or inter-species scattering length. Consequently, in the dilute limit, the Bardeen-Cooper-Shrieffer (BCS) pairing state of bosons can be formed with weakly-attractive inter-species and repulsive intra-species interactions. The quasiparticle excitation energies are anisotropic due to spin-orbit coupling. This BCS paring state is energetically favored over Bose-Einstein condensation (BEC) of atoms at low densities. As the density increases, there is a first-order transition from the BCS to BEC states.