Pair condensation in a dilute Bose gas with Rashba spin–orbit coupling

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 Bose gas with attractive intra-species and repulsive inter-species interactions. The critical temperature of Rashbon condensation is about six times smaller than the Bose–Einstein condensation transition temperature of an ideal Bose gas. Due to the Rashba SOC, excitations in the Rashbon condensation phase are anisotropic in momentum space. (paper)