Interface fluctuations and kinetics of nucleation in helium at ultralow temperatures

Abstract

Interface fluctuations and kinetics of nucleating droplets are studied in {sup 4}He and {sup 3}He-{sup 4}He mixtures at ultralow temperatures in the dissipationless regime. We firstly discuss the droplet number density arising as quantum fluctuations and secondly derive the Rayleigh-Plesset equation for a droplet in a metastable fluid. This equation, which is well-known in classical hydrodynamics, governs kinetics of domain growth at very low temperatures. Thirdly, the quantum nucleation rate is shown to be much enhanced by high-frequency acoustic or electric field, however small its amplitude is, when the period of oscillation 2{pi}/{omega} is shorter than the time {tau}{sub s} of tunnelling through the potential barrier. Fourthly, we examine equilibrium fluctuations of a planar interface which macroscopically separates two phases. The correlation function of the interface displacement is shown to cross over from the classical expression into a newly found quantum expression as the temperature is lowered.