Spin current generation and relaxation in a quenched spin-orbit-coupled Bose-Einstein condensate

TL;DR

This paper investigates how synthetic spin-orbit coupling and atomic interactions influence spin transport and relaxation in a Bose-Einstein condensate, revealing enhanced damping, reduced thermalization, and collective excitations.

Contribution

It provides the first experimental and theoretical analysis of spin transport effects in a charge-neutral bosonic system with synthetic SOC.

Findings

SOC enhances spin-dipole mode damping

SOC reduces thermalization and condensate fraction

Generation of collective shape oscillations observed

Abstract

Understanding the effects of spin-orbit coupling (SOC) and many-body interactions on spin transport is important in condensed matter physics and spintronics. This topic has been intensively studied for spin carriers such as electrons but barely explored for charge-neutral bosonic quasiparticles (including their condensates), which hold promises for coherent spin transport over macroscopic distances. Here, we explore the effects of synthetic SOC (induced by optical Raman coupling) and atomic interactions on the spin transport in an atomic Bose-Einstein condensate (BEC), where the spin-dipole mode (SDM, actuated by quenching the Raman coupling) of two interacting spin components constitutes an alternating spin current. We experimentally observe that SOC significantly enhances the SDM damping while reducing the thermalization (the reduction of the condensate fraction). We also observe generation of BEC collective excitations such as shape oscillations. Our theory reveals that the SOC-modified interference, immiscibility, and interaction between the spin components can play crucial roles in spin transport.