Probing superfluidity in a quasi two-dimensional Bose gas through its local dynamics

TL;DR

This paper provides direct evidence of superfluidity in a quasi two-dimensional Bose gas by analyzing its local dynamical response, revealing phase boundaries and fluid coupling effects.

Contribution

It introduces a novel local correlation analysis method to probe inhomogeneous Bose gases and identify superfluid and thermal phases.

Findings

Identification of superfluid and thermal phases within the gas

Localization of the BKT crossover boundary

Observation of enhanced damping due to fluid coupling

Abstract

We report direct evidence of superfluidity in a quasi two-dimensional Bose gas by observing its dynamical response to a collective excitation. Relying on a novel local correlation analysis, we are able to probe inhomogeneous clouds and reveal their local dynamics. We identify in this way the superfluid and thermal phases inside the gas and locate the boundary at which the Berezinskii--Kosterlitz--Thouless crossover occurs. This new analysis also allows to evidence the coupling of the two fluids which induces at finite temperatures damping rates larger than the usual Landau damping.