Critical Casimir Effect in 3He-4He films

TL;DR

This paper investigates the universal thermodynamic Casimir effect in 3He-4He wetting films near the tricritical point, using models that capture the relevant universality class, and compares theoretical predictions with experimental data.

Contribution

It provides a theoretical analysis of Casimir forces in 3He-4He films with nonsymmetric boundary conditions, highlighting the crossover behavior and agreement with experiments.

Findings

Casimir forces can be repulsive under nonsymmetric boundary conditions.

Theoretical results match experimental measurements.

Logarithmic corrections are significant in the analysis.

Abstract

Universal aspects of the thermodynamic Casimir effect in wetting films of 3He-4He mixtures near their bulk tricritical point are studied within suitable models serving as representatives of the corresponding universality class. The effective forces between the boundaries of such films arising from the confinement are calculated along isotherms at several fixed concentrations of 3He. Nonsymmetric boundary conditions impose nontrivial concentration profiles leading to repulsive Casimir forces which exhibit a rich behavior of the crossover between the tricritical point and the line of critical points. The theoretical results agree with published experimental data and emphasize the importance of logarithmic corrections.