Hydrodynamic modes of partially condensed Bose mixtures

TL;DR

This paper extends hydrodynamic theory to two-component Bose mixtures, revealing new collective modes involving both components and analyzing their dispersions with thermodynamic inputs.

Contribution

It introduces a generalized hydrodynamic framework for binary Bose mixtures, including spin-drag effects and predicting novel collective excitations.

Findings

Identification of new collective modes involving both components

Derivation of dispersion relations using thermodynamic data

Inclusion of viscous coupling effects in the hydrodynamic description

Abstract

We generalize the Landau-Khalatnikov hydrodynamic theory for superfluid helium to two-component (binary) Bose mixtures at arbitrary temperatures. In particular, we include the spin-drag terms that correspond to viscous coupling between the clouds. Therefore, our theory not only describes the usual collective modes of the individual components, e.g., first and second sound, but also results in new collective modes, where both constituents participate. We study these modes in detail and present their dispersions using thermodynamic quantities obtained within the Popov approximation.