Interface fluctuations and stratification in 3He-4He mixture films

Abstract

Starting from the stratified state induced by the substrate Van der Waals field, we develop a phenomenological model for « thin » mixture films in terms of a multilayer description. Introducing fluctuations in this multilayer system allows us to describe interface excitations which are found to destabilize the stratified structure in a film thickness range which shrinks to zero as the temperature is reduced. This behaviour is observed in our third sound measurements of 3He-4He mixture films which study both the thickness and temperature dependence of the stratification-homogeneous transition. A quantitative agreement between the theory and our experiments is achieved by improving the mean field description with the introduction of a dynamical argument involving short wavelength fluctuations.