Instabilities of Bosonic Spin Currents in Optical Lattices

TL;DR

This paper investigates the stability of spin currents in two-component bosonic systems in optical lattices across different interaction regimes, revealing a regime of dynamical instability between superfluid and Mott insulator phases.

Contribution

It provides a comprehensive analysis of spin current instabilities using Bogoliubov and Gutzwiller theories across various regimes, identifying a novel instability regime.

Findings

No instabilities in deep superfluid and Mott phases predicted by models.

Identification of a dynamical instability regime between superfluid and Mott phases.

Results are relevant for experimental realization of stable Neel states in ultracold bosons.

Abstract

We analyze the dynamical and energetic instabilities of spin currents in a system of two-component bosons in an optical lattice, with a particular focus on the Neel state. We consider both the weakly interacting superfluid and the strongly interacting Mott insulating limits as well as the regime near the superfluid-insulator transition and establish the criteria for the onset of these instabilities. We use Bogoliubov theory to treat the weakly interacting superfluid regime. Near the Mott transition, we calculate the stability phase diagram within a variational Gutzwiller wavefunction approach. In the deep Mott limit we discuss the emergence of the Heisenberg model and calculate the stability diagram within this model. Though the Bogoliubov theory and the Heisenberg model (appropriate for deep superfluid and deep Mott phase respectively) predict no dynamical instabilities, we find, interestingly, between these two limiting cases there is a regime of dynamical instability. This result is relevant for the ongoing experimental efforts to realize a stable Neel-ordered state in multi-component ultracold bosons.