Thinning of superfluid films below the critical point

TL;DR

This paper investigates the attractive Casimir-like force in superfluid helium films below the lambda transition, using a mean-field approach with critical fluctuation renormalization to explain experimental observations.

Contribution

It introduces a simple mean-field model renormalized by critical fluctuations that qualitatively reproduces the observed Casimir force below the lambda point.

Findings

The model aligns with experimental scaling functions.

It explains the magnitude of the force immediately below the lambda point.

The approach provides a qualitative understanding of the force behavior.

Abstract

Experiments on $^4$He films reveal an attractive Casimir-like force at the bulk $\lambda$-point, and in the superfluid regime. Previous work has explained the magnitude of this force at the $\lambda$ transition and deep in the superfluid region but not the substantial attractive force immediately below the $\lambda$-point. Utilizing a simple mean-field calculation renormalized by critical fluctuations we obtain an effective Casimir force that is qualitatively consistent with the scaling function $\vartheta$ obtained by collapse of experimental data.