Casimir forces, surface fluctuations, and thinning of superfluid films

TL;DR

This paper investigates the thinning of superfluid helium films at the lambda transition, proposing that surface fluctuations, in addition to Casimir forces, significantly contribute to the observed effects.

Contribution

The study introduces the role of surface fluctuations as a key factor in film thinning, extending beyond the traditional Casimir force explanation.

Findings

Surface fluctuations produce an additional attractive force.

This force is larger than the Casimir force alone.

The combined effect explains the experimental thinning of superfluid films.

Abstract

Recent experiments on the wetting of $^{4}$He have shown that the film becomes thinner at the $\lambda$ transition, and in the superfluid phase. The difference in thickness above and below the transition has been attributed to a Casimir interaction which is a consequence of a broken continuous symmetry in the bulk superfluid. However, the observed thinning of the film is larger than can be accounted by this Casimir force. We show that surface fluctuations give rise to an additional force, similar in form but larger in magnitude, which may explain the observations.