Recent Progress in Thin 3He–4He Films

Abstract

We review recent work on the properties of 3He–4He thin film mixtures. The subject is introduced by reviewing the contributions made by Gasparini and co-workers. In the first part of this survey, we examine a microscopic calculation of the effects that an adsorbed 3He component has on the collective excitations associated with a 4He film, third sound. The work in question computes the change in the third sound velocity due to adding 3He, and we can compare this with existing experiment. For small 3He coverage, the change in the third sound speed depends on the derivatives of the species chemical potentials with respect to the areal density. The microscopic calculation shows oscillations in the third sound speed that reflect the layered structure of the film. In the second part of this survey, we concentrate on the 3He component. An important impact of the 4He environment is to change the bare mass in the limit of zero 3He concentration to a hydrodynamic mass. Quasiparticle interactions are introduced through the Landau parameters. Our Landau parameters are determined by fitting s-wave and p-wave T-matrix components using experimental results for the effective mass and the spin susceptibility. We can then predict the thermodynamic behavior of the mixture films at finite polarization, and in addition we can predict the spectrum of zero-sound excitations at all polarizations.