Sound propagation in striped supersolid cold gases at zero temperature

TL;DR

This paper develops a hydrodynamic framework to analyze sound propagation in stripe phases of ultracold dipolar gases and spin-orbit-coupled BECs at zero temperature, highlighting differences due to Galilean invariance.

Contribution

It introduces a unified hydrodynamic approach applicable to both platforms, accounting for symmetry differences and predicting anisotropic sound spectra.

Findings

Both systems exhibit two anisotropic sound modes due to symmetry breaking.

The spin-orbit case lacks Galilean invariance, affecting the current equations.

Comparison with smectic-A liquid crystals reveals similarities in sound behavior.

Abstract

We present a unified hydrodynamic approach for the sound propagation in the stripe phases realized in ultracold dipolar gas and spin-orbit-coupled BEC platforms at zero temperature. Despite the deep difference of the two platforms at a microscopic level, a similar hydrodynamic description can be formulated at a macroscopic level. The main difference between the two platforms is the lack of Galilean invariance in the spin-orbit case, resulting in a different identification of the normal (nonsuperfluid) component of the density, which leads to new terms in the equation for the current. In both cases the spectrum comprises two sounds, reflecting the spontaneous breaking of the U(1) and translational symmetries. Both sounds exhibit an anisotropic behavior. A comparison with the first and second sounds of the smectic-A liquid crystal is also presented.