Coherence-length effects on the nucleation of superfluid transitions in liquid-helium mixtures

A theory of the nucleation of superfluid transitions near container walls of $^{3}\mathrm{He}$-$^{4}\mathrm{He}$ mixtures is developed. The theory uses a local-continuum model, which accounts for wall-potential-induced concentration and pressure gradients, supplemented by an important coherence-length correction to account for the finite thickness of the nucleation films. An excellent one-parameter fit to the available experimental data is obtained. The theory provides support for the concept of universality in phase-transition phenomena.