Critical velocities in two-component superfluid Bose gases

TL;DR

This paper investigates the critical velocities in two-component superfluid Bose gases using the Landau criterion, revealing how the velocities of each component relate to elementary excitations and how confinement affects these velocities.

Contribution

It introduces a relation between the critical velocities of two-component Bose gases and generalizes the analysis to confined condensates.

Findings

Critical velocities depend on elementary excitation phase velocities.

One or both components can exceed the elementary excitation velocity.

Maximum critical velocity occurs when the other component is stationary.

Abstract

On the ground of the Landau criterion we study the behavior of critical velocities in a superfluid two-component Bose gas. It is found that under motion of the components with different velocities the velocity of each component should not be lower than a minimum phase velocity of elementary excitations (s_). The Landau criterion yields a relation between the critical velocities of the components (v_{c1}, v_{c2}). The velocity of one or even both components may exceed s_. The maximum value of the critical velocity of a given component can be reached when the other component does not move. The approach is generalized for a two-component condensate confined in a cylindrical harmonic potential. PACS numbers: 03.75.Kk,03.75.Mn