Chiral spin superfluidity and spontaneous spin Hall effect of interacting bosons

TL;DR

This paper predicts a new chiral spin superfluid state in ultracold bosonic gases with spontaneous spin Hall effects, arising from quantum fluctuations in degenerate bands, and proposes experimental detection methods.

Contribution

It introduces a universal quantum 'order by disorder' mechanism leading to chiral spin superfluidity with novel properties in spinor Bose gases.

Findings

Discovery of a chiral spin superfluid with spontaneous spin Hall effect

Prediction of staggered spin loop currents in real space

Proposal of Bloch oscillations for state preparation

Abstract

Recent experiments on ultracold atoms in optical lattices have synthesized a variety of tunable bands with degenerate double-well structures in momentum space. Such degeneracies in the single particle spectrum strongly enhance quantum fluctuations, and may lead to exotic many-body ground states. Here we consider weakly interacting spinor Bose gases in such bands, and discover a universal quantum "order by disorder" phenomenon which selects a novel chiral spin superfluid with remarkable properties such as spontaneous anomalous spin Hall effect and momentum space antiferromagnetism. For bosons in the excited Dirac band of a hexagonal lattice, such a state supports staggered spin loop currents in real space. We show that Bloch oscillations provide a powerful dynamical route to quantum state preparation of such a chiral spin superfluid. Our predictions can be readily tested in spin resolved time-of-flight experiments.