Abstract
Experiments and theories describing the metastable phases of liquid and solid $$^4$$ He are presented and discussed. For the case of metastable liquid $$^4$$ He with respect to its gaseous phase, it is shown that different measurements of its destabilization threshold (cavitation threshold) and their comparisons to available theories reveal that the nucleation mechanism is not totally understood. Then experiments measuring typical lifetime of cavitation bubbles in He I and He II are shortly considered showing the important role of heat transport mechanism during their collapse. Finally for liquid $$^4$$ He, its metastability with respect to its solid phase and the possibility of the liquid destabilization due to the vanishing of the roton gap is presented. The last part of the review is devoted to metastable solid $$^4$$ He with respect to its liquid phase. The first experimental production of such a state is described and its destabilization limit possibly invoking the creation and proliferation of crystalline defects is discussed.
Highlights
Achieving a metastable phase of liquid 4He consists in bringing a sample of liquid 4He at a temperature and a pressure where the thermal equilibrium phase is not the liquid phase but rather the solid one or the gaseous one
Applying this method to determine the density of metastable liquid 4He at the homogeneous cavitation threshold ρcav at T ∼ 1 K, we found that ρcav = 0.1338 ± 0.0002 g.cm−3 [20, 13]
Regarding metastable liquid 4He and cavitation in it, recent measurements of the cavitation threshold have reopened the debate on heterogeneous nucleation in this perfectly wetting system
Summary
Achieving a metastable phase of (for instance) liquid 4He consists in bringing a sample of liquid 4He at a temperature and a pressure (or density) where the thermal equilibrium phase is not the liquid phase but rather the solid one or the gaseous one. Pure liquid and solid 4He appear to be the ideal candidates for testing homogeneous nucleation theory In this short review, I shall discuss experiments and theories describing the metastable phases of bulk liquid and solid 4He. Metastable phases of condensed 4He confined in porous media have been investigated with specific detection methods[1, 2, 3]. The essential advantage of this acoustic method is that it can produce large pressure/density swings far from any interface (walls of the container and of the transducer) and in a small volume (the acoustic focus) of the bulk of the sample These two points strongly reduce the chance of generating heterogeneous nucleation events and make possible a deep exploration of the metastable state up to a point where homogeneous nucleation is expected to be observed. Experimental results regarding the stability limit of the solid suggest that crystalline defects could play an important role in the destabilization of the solid
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