Emergence of a spin microemulsion in spin-orbit coupled Bose-Einstein condensates

TL;DR

This paper predicts a novel spin microemulsion phase in spin-orbit coupled Bose-Einstein condensates, characterized by undulating spin domains and a transition from a stripe phase to a disordered fluid at finite temperature.

Contribution

First numerical prediction of a spin microemulsion phase in 2D spinor Bose-Einstein condensates with Rashba spin-orbit coupling, revealing a new intermediate structured phase.

Findings

Identification of a spin microemulsion phase with undulating spin domains.

Observation of a transition from a supersolid stripe phase to a disordered microemulsion.

Finite-temperature phase diagram showing the microemulsion as an intermediate phase.

Abstract

We report the first numerical prediction of a "spin microemulsion" -- a phase with undulating spin domains resembling classical bicontinuous oil-water-surfactant emulsions -- in two-dimensional systems of spinor Bose-Einstein condensates with isotropic Rashba spin-orbit coupling. Using field-theoretic numerical simulations, we investigated the melting of a low-temperature stripe phase with supersolid character and find that the stripes lose their superfluidity at elevated temperature and undergo a Kosterlitz--Thouless-like transition into a spin microemulsion. Momentum distribution calculations highlight a thermally broadened occupation of the Rashba circle of low-energy states with macroscopic and isotropic occupation around the ring. We provide a finite-temperature phase diagram that positions the emulsion as an intermediate, structured isotropic phase with residual quantum character before transitioning at higher temperature into a structureless normal fluid.