Modulational instability in binary spin-orbit-coupled Bose-Einstein condensates

TL;DR

This paper investigates how spin-orbit coupling influences modulation instability in two-component Bose-Einstein condensates, revealing that SOC induces instability regardless of traditional immiscibility conditions, suggesting a striped ground state.

Contribution

It demonstrates that spin-orbit coupling fundamentally alters the modulation instability conditions in binary BECs, always inducing instability and potentially leading to striped phases.

Findings

SOC strongly modifies the MI condition in binary BECs.

Binary BECs are always subject to MI under SOC.

Ground state likely forms a striped phase due to SOC effects.

Abstract

We study modulation instability (MI) of flat states in two-component spin-orbit-coupled (SOC) Bose-Einstein condensates (BECs) in the framework of coupled Gross-Pitaevskii equations for two components of the pseudospinor wave function. The analysis is performed for equal densities of the components. Effects of the interaction parameters, Rabi coupling, and SOC on the MI are investigated. In particular, the results demonstrate that the SOC strongly alters the commonly known MI (immiscibility) condition, $g_{12} > g_{1} g_{2}$, for the binary superfluid with coefficients $g_{1,2}$ and $g_{12}$ of the intra- and interspecies repulsive interactions. In fact, the binary BEC is always subject to the MI under the action of the SOC, which implies that the ground state of the system is plausibly represented by a striped phase.