Rashba-type Spin-orbit Coupling in Bilayer Bose-Einstein Condensates

TL;DR

This paper proposes a novel method to generate Rashba-type spin-orbit coupling in ultracold atom Bose-Einstein condensates using a bilayer setup with cyclic spin-layer state transitions, revealing diverse ground states including skyrmion lattices.

Contribution

It introduces a new bilayer scheme for creating Rashba SOC in BECs, analyzing ground states and phase diagrams with theoretical and variational methods.

Findings

Diverse ground-state phase diagram with various phases.

Spontaneous formation of skyrmion and antiskyrmion lattices.

Ground states include plane-wave and standing-wave phases.

Abstract

We explore a new way of producing the Rashba spin-orbit coupling (SOC) for ultracold atoms by using a two-component (spinor) atomic Bose-Einstein condensate (BEC) confined in a bilayer geometry. The SOC of the Rashba type is created if the atoms pick up a {\pi} phase after completing a cyclic transition between four combined spin-layer states composed of two spin and two layer states. The cyclic coupling of the spin-layer states is carried out by combining an intralayer Raman coupling and an interlayer laser assisted tunneling. We theoretically determine the ground-state phases of the spin-orbit-coupled BEC for various strengths of the atom-atom interaction and the laser-assisted coupling. It is shown that the bilayer scheme provides a diverse ground-state phase diagram. In an intermediate range of the atom-light coupling two interlacing lattices of half- skyrmions and half-antiskyrmions are spontaneously created. In the strong-coupling regime, where the SOC of the Rashba-type is formed, the ground state represents plane-wave or standing-wave phases depending on the interaction between the atoms. A variational analysis is shown to be in a good agreement with the numerical results.