Study of Nucleation Phenomena in ^3He-^4He Liquid Mixtures-Quantum Nucleation-

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Quantum nucleation is a kind of macroscopic quantum tunneling phenomena, accompanying the decay of metastable system described with a macroscopic variable. The concept of quantum nucleation is currently used in varioious fields of physics. So it is extremely important to obtain the corroborative evidence of the phenomenon.We made the first systematic studies of the low temperature phase-separation kinetics, down to 0.4mK in the two-component metastable system as a supersaturated liquid^3He-^4He mixture of dilute phase. The experiments determined the values of critical supersaturation, DELTAchi3, cr, as a function of temperature from 0.4mK up to 160mK.Here, DELTAchi3, cr, is the upperlimit of the deviation of ^3He concentration of dilute phase from the equilibrium value. The values of DELTAchi3, cr, becomes almost independent of temperature below about 10mK.This fact strongly suggests that the phase-separation is triggered by quantum nucleation, at least in this temperature region.Another interesting feature of our results is that DELTAchi3, cr, increases with temperature above about 10mK.This conflicts with a simple expectation of the crossover consideration from the quantum to the classical regime. Such behavior may qualitatively be understood by taking into account the effect of dissipation on the tunneling probability.In theoretical side, we re-examined the Lifshitz-Kagan model of macroscopic quantum nucleation. It is shown that the R dependence of the moss has a profound effect on the nucleation rate. Here, R is radius of the virtual nucleus. We gave a sketch to deduce the Lifshitz-Kagan model from a generalized non-linear Schrodinger field model.