Universal phase structure of dilute Bose gases with Rashba spin-orbit coupling

TL;DR

This paper reveals that dilute Bose gases with Rashba spin-orbit coupling exhibit a universal phase structure characterized by angle-dependent interactions, leading to condensation at opposite momenta and a pair condensation instability, regardless of microscopic details.

Contribution

It demonstrates the universal, angle-dependent renormalization of interactions and the resulting phase behavior in dilute Bose gases with Rashba spin-orbit coupling, independent of microscopic interactions.

Findings

Ground state involves condensation at two opposite momenta.

Finite systems exhibit fragmented condensates.

Nonzero-temperature instability toward pair condensation.

Abstract

A Bose gas subject to a light-induced Rashba spin-orbit coupling possesses a dispersion minimum on a circle in momentum space; we show that kinematic constraints due to this dispersion cause interactions to renormalize to universal, angle-dependent values that govern the phase structure in the dilute-gas limit. We find that, regardless of microscopic interactions, (a) the ground state involves condensation at two opposite momenta, and is, in finite systems, a fragmented condensate; and (b) there is a nonzero-temperature instability toward the condensation of pairs of bosons. We discuss how our results can be reconciled with the qualitatively different mean-field phase diagram, which is appropriate for dense gases.