Crossover between Kelvin-Helmholtz and counter-superflow instabilities in two-component Bose-Einstein condensates

TL;DR

This paper investigates the crossover between Kelvin-Helmholtz and counter-superflow instabilities in two-component Bose-Einstein condensates, analyzing their conditions, emergence, and dynamics through mean-field and Bogoliubov methods.

Contribution

It identifies the conditions under which each instability dominates and demonstrates their dynamics in rotating trapped condensates, revealing the crossover behavior.

Findings

Kelvin-Helmholtz instability dominates when interface thickness is small.

Counter-superflow instability dominates when interface thickness is large.

Instabilities occur in both immiscible and externally induced interface systems.

Abstract

Dynamical instabilities at the interface between two Bose--Einstein condensates that are moving relative to each other are investigated using mean-field and Bogoliubov analyses. Kelvin--Helmholtz instability is dominant when the interface thickness is much smaller than the wavelength of the unstable interface mode, whereas the counter-superflow instability becomes dominant in the opposite case. These instabilities emerge not only in an immiscible system but also in a miscible system where an interface is produced by external potential. Dynamics caused by these instabilities are numerically demonstrated in rotating trapped condensates.