Sound modes in collisional superfluid Bose gases

TL;DR

This paper provides a theoretical analysis of sound modes in collisional superfluid Bose gases across different dimensions, revealing hybridization phenomena in 2D and offering insights into experimental observations near the BKT transition.

Contribution

It introduces a refined superfluid density calculation within Landau's two-fluid hydrodynamics, explaining sound mode behavior and matching recent 2D experimental data.

Findings

Hybridization of first and second sound in D≥2

Accurate superfluid density modeling near BKT transition

No hybridization observed in 1D, indicating future research needed

Abstract

We theoretically investigate sound modes in a weakly-interacting collisional Bose gas in $D$ dimensions. Using the Landau's two-fluid hydrodynamics and working within the Bogoliubov theory, we observe the hybridization of the first and second sound modes for $D\ge 2$. To model the recent measurements of the sound velocities in 2D, obtained in the weakly-interacting regime and around the Berezinskii-Kosterlitz-Thouless transition temperature, we derive a refined calculation of the superfluid density, finding a fair agreement with the experiment. In the 1D case, for which experimental results are currently unavailable, we find no hybridization, triggering the necessity of future investigations. Our analysis provides a systematic understanding of sound propagation in a collisional weakly-interacting Bose gas in $D$ dimensions.