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

一级相变是作为均匀亚稳介质（核）中的涨落的结果的从亚稳相到稳定相的状态变化。对于成核，由于界面的产生而存在势垒。通常，这种涨落是热涨落。然而，在与势垒高度相比极低的温度区域中，热波动不再有效。如果在这种情况下我们仍然有任何一级相变，那么成核必然是由于量子隧穿。量子成核是一种宏观量子现象，为了研究量子成核的可能性，在160 mK ~ 400 μ K温度范围内，研究了过饱和^3He-^4He混合液在稀相中的分解过程。临界过饱和度的观测量在低于约10 mK时变得几乎与温度无关，而在高于约10 mK时则增加。这种与温度无关的行为表明，我们至少在10 mK以下处于量子状态.在大约10 mK以上的行为与从量子到经典状态的交叉考虑的简单期望相冲突。这一事实表明耗散效应在宏观量子现象中的重要性。

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.