Expansion of Liquid 4He Through the Lambda Transition

TL;DR

This study investigates vortex formation in liquid helium-4 during rapid cooling, finding that most vortices originate from conventional flow rather than the Kibble mechanism, challenging previous interpretations.

Contribution

The paper introduces a redesigned experimental setup that minimizes flow-induced vortices, providing clearer evidence on the origin of vortices during the superfluid transition.

Findings

Vortex line densities are significantly lower with the new cell.

Most vortices in earlier experiments likely resulted from flow, not the Kibble mechanism.

The observed vortex densities are much less than theoretical predictions.

Abstract

Zurek suggested [Nature 317 (1985) 505] that the Kibble mechanism, through which topological defects such as cosmic strings are believed to have been created in the early Universe, can also result in the formation of topological defects in liquid 4He, i.e. quantised vortices, during rapid quenches through the superfluid transition. Preliminary experiments [Hendry et al, Nature 368 (1994) 315] seemed to support this idea in that the quenches produced the predicted high vortex-densities. The present paper describes a new experiment incorporating a redesigned expansion cell that minimises vortex creation arising from conventional hydrodynamic flow. The post-quench line-densities of vorticity produced by the new cell are no more than 10^10 m^{-2}, a value that is at least two orders-of-magnitude less than the theoretical prediction. We conclude that most of the vortices detected in the original experiment must have been created through conventional flow processes.