Superfluid fraction in an interacting spatially modulated Bose-Einstein condensate

TL;DR

This paper investigates how a one-dimensional periodic potential affects the superfluid density of a dilute Bose-Einstein condensate, combining theoretical bounds and experimental data to understand the role of interactions and symmetry breaking.

Contribution

It provides a combined theoretical and experimental analysis of superfluid fraction quenching in a BEC due to translational symmetry breaking by a periodic potential.

Findings

Superfluid fraction decreases with increasing lattice depth.

Leggett's bound and sound velocity anisotropy agree on superfluid fraction estimates.

Two-body interactions significantly influence superfluidity in modulated BECs.

Abstract

At zero temperature, a Galilean-invariant Bose fluid is expected to be fully superfluid. Here we investigate theoretically and experimentally the quenching of the superfluid density of a dilute Bose-Einstein condensate due to the breaking of translational (and thus Galilean) invariance by an external 1D periodic potential. Both Leggett's bound fixed by the knowledge of the total density and the anisotropy of the sound velocity provide a consistent determination of the superfluid fraction. The use of a large-period lattice emphasizes the important role of two-body interactions on superfluidity.