Sound, superfluidity and layer compressibility in a ring dipolar supersolid

TL;DR

This paper investigates the excitation of Goldstone modes in a ring-shaped dipolar supersolid Bose-Einstein condensate, analyzing sound velocities, layer compressibility, and superfluid fraction through hydrodynamic theory and numerical simulations.

Contribution

It introduces a protocol to excite and analyze Goldstone modes in a dipolar supersolid ring, providing new insights into its sound velocities and superfluid properties.

Findings

Identification of two longitudinal sound velocities in the supersolid phase

Determination of layer compressibility modulus

Estimation of superfluid fraction consistent with Leggett's theory

Abstract

We propose a protocol to excite the Goldstone modes of a supersolid dipolar Bose-Einstein condensed gas confined in a ring geometry. By abruptly removing an applied periodic modulation proportional to cos($\varphi$), where $\varphi$ is the azimuthal angle, we explore the resulting oscillations of the gas, by solving the extended Gross-Pitaevskii equation. The value of the two longitudinal sound velocities exhibited in the supersolid phase are analyzed using the hydrodynamic theory of supersolids at zero temperature. This approach allows for the determination of the layer compressibility modulus as well as of the superfluid fraction $f_S$, in agreement with the Leggett estimate of the non-classical moment of inertia.