Quantum Nucleation

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Quantum nucleation is a kind of macroscopic quantum phenomenon accompanying the decay of metastable system described with a macroscopic variable, that is, the radius of a nucleus of the stable phase. The concept of quantum nucleation is currently applied in various field of physics. So, it is extremely important to obtain the unambiguous evidence of the phenomenon.The system of superfluid supersaturated ィイD13ィエD1He-ィイD14ィエD1He mixture is apparently the most prominent and unique system for observing the bulk quantum nucleation, in a condensed matter. Firstly, wall effects may be negligible because of the difference of zero-point energy between ィイD13ィエD1He and ィイD14ィエD1He atoms. That is, any surface is unlikely to be effective in nucleating the ィイD13ィエD1He-concentrated phase (c-phase). Secondly, our invented method to realize a supersaturated state of the ィイD13ィエD1He-dilute phase (d-phase) is a pressure sweep method, in which we can control the sweep rate so slowly that the almost quasis … More tatic condition is realized.Here, we report the results of the systematic study of the phase separation from supersaturated superfluid ィイD13ィエD1He-ィイD14ィエD1He mixtures of d-phase. The amount of critical supersaturation, ΔXィイD23ィエD2,cr was determined in the wide ranges of the temperature (400μK - 500mK) and the pressure (0 - 8kg・f/cmィイD12ィエD1). With the data we constructed the surface of critical supersaturation, ΔXィイD23ィエD2,cr (T,P), which enable us to recognize the overall features of critical supersaturation in superfluid ィイD13ィエD1He-ィイD14ィエD1He mixtures. The main specific features observed are as follows.(i) Below about 10mK, ΔXィイD23ィエD2,cr is almost independent of temperature.(ii) Above about 10mK, ΔXィイD23ィエD2,cr increases with temperature.The first fact was analyzed with the theory by Nakamura et al. semi-quantitably. It is shown that the phase-separation observed by us below about 10mK is triggered by quantum nucleation. The second fact suggests the effect of dissipation on the nucleation process. Burmistrov and Satoh theoretically discussed that effect by considering the second sound mode and the diffusion of ィイD13ィエD1He atoms in the d-phase. Our recent experimental investigation on the dynamics of the interface between the c-and d-phases strongly supports that consideration. Less