Sound propagation in a uniform superfluid two-dimensional Bose gas

TL;DR

This study investigates sound propagation in a uniform 2D Bose gas, demonstrating the behavior of sound modes across superfluid and normal phases and validating hydrodynamic models in the superfluid regime.

Contribution

The paper provides experimental characterization of sound modes in a 2D Bose gas and confirms hydrodynamic descriptions in the superfluid phase.

Findings

Sound speed matches two-fluid hydrodynamic predictions in the superfluid phase

Weak damping explained by scattering with thermal excitations

Sound becomes strongly damped in the normal phase

Abstract

In superfluid systems several sound modes can be excited, as for example first and second sound in liquid helium. Here, we excite propagating and standing waves in a uniform two-dimensional Bose gas and we characterize the propagation of sound in both the superfluid and normal regime. In the superfluid phase, the measured speed of sound is well described by a two-fluid hydrodynamic model, and the weak damping rate is well explained by the scattering with thermal excitations. In the normal phase the sound becomes strongly damped due to a departure from hydrodynamic behavior.