Spontaneous ferromagnetism in the spinor Bose gas with Rashba spin-orbit coupling

TL;DR

This paper demonstrates that even minimal attractive interactions in a Rashba spin-orbit coupled two-component Bose gas can lead to spontaneous ferromagnetism and a ferromagnetic Bose-Einstein condensate below a critical temperature.

Contribution

It reveals the emergence of spontaneous ferromagnetism in a spinor Bose gas with Rashba coupling due to arbitrarily small attractive interactions, a novel phenomenon.

Findings

Spontaneous ferromagnetism occurs with any attractive interaction below T_c.

The spectrum has a unique minimum aligned with the magnetization.

Bosons condense into a ferromagnetic Bose-Einstein condensate below T_c.

Abstract

We show that in the two-component Bose gas with Rashba spin-orbit coupling an arbitrarily small attractive interaction between bosons with opposite spin induces spontaneous ferromagnetism below a finite critical temperature $T_c$. In the ferromagnetic phase the single-particle spectrum exhibits a unique minimum in momentum space in the direction of the magnetization. For sufficiently small temperatures below $T_c$ the bosons eventually condense into the unique state at the bottom of the spectrum, forming a ferromagnetic Bose-Einstein condensate.