Rashbon condensation in a Bose gas with Rashba spin-orbit coupling

TL;DR

This paper demonstrates that Rashba spin-orbit coupling enables bound states (Rashbons) in a two-component Bose gas, leading to a novel Rashbon condensate with unique properties and anisotropic excitations.

Contribution

It introduces the concept of Rashbon formation and condensation in Bose gases with Rashba SOC, revealing new bound states and phase behavior not previously known.

Findings

Rashbons form with any intra-species scattering length.

Degeneracy of Rashbons is lifted at finite momentum, resulting in different effective masses.

Rashbon condensation has a critical temperature about six times lower than ideal BEC.

Abstract

We show that in a two-component Bose gas with Rashba spin-orbit coupling (SOC) two atoms can form bound states (Rashbons) with any intra-species scattering length. At zero center-of-mass momentum there are two degenerate Rashbons due to time-reversal symmetry, but the degeneracy is lifted at finite in-plane momentum with two different effective masses. A stable Rashbon condensation can be created in a dilute system with weakly attractive intra-species and repulsive inter-species interactions. The critical temperature of Rashbon condensation is about six times smaller than the BEC transition temperature of an ideal Bose gas. Due Rashba SOC, excitations in the Rashbon condensation phase are anisotropic in momentum space.