Beyond the Landau Criterion for Superfluidity

TL;DR

This paper challenges the traditional Landau criterion for superfluidity by demonstrating that the critical velocity depends on defect strength and shape, showing it can vanish at high defect intensities.

Contribution

It provides a quantitative analysis of how defect characteristics influence superfluid critical velocity, combining numerical simulations with an analytical model.

Findings

Critical velocity decreases with increasing defect strength.

Critical velocity vanishes at a critical defect intensity.

Superfluid stability is sensitive to defect shape and strength.

Abstract

According to the Landau criterion for superfluidity, a Bose-Einstein condensate flowing with a group velocity smaller than the sound velocity is energetically stable to the presence of perturbing potentials. We found that this is strictly correct only for vanishingly small perturbations. The superfluid critical velocity strongly depends on the strength and shape of the defect. We quantitatively study, both numerically and with an approximate analytical model, the dynamical response of a one-dimensional condensate flowing against an istantaneously raised spatially periodic defect. We found that the critical velocity $v_c$ decreases by incresing the strength of the defect $V_0$, up to to a critical value of the defect intensity where the critical velocity vanishes.