Nucleation in Supersaturated ^3He-^4He Liquid Mixtures - Quantum Effects in First Order Phase Transition -

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A first order phase transition is the change of state from a metastable to a stable phase as the result of fluctuation in a homogeneous metastable medium, nuclei. For the nucleation, there is a potential barrier due to the creation of an interface. Usually, the fluctuation is the thermal fluctuation. However, in a temperature region extremely low compared with barrier height, the thermal fluctuation is no longer effective. If we still have any first order phase transition in such a situation, the nucleation must be due to the quantum tunneling. Quantum nucleation is a kind of macroscopic quantum phenomenon.In order to investigate the possibility of the quantum nucleation, the decomposition of supersaturated ^3He-^4He liquid mixtures in the dilute phase has been studied in the temperature range from 160 mK down to 400 muK. The observed amount of critical supersaturation becomes almost independent of temperature below about 10 mK, while it increases above about 10 mK. The temperature- independent behavior suggests that we are in the quantum regime at least below about 10 mK. The behavior above about 10 mK conflicts with a simple expectation of the crossover consideration from the quantum to the classical regime. This fact suggests the importance of the effect of dissipation in macroscopic quantum phenomenon.