4He-crystallization via quantum tunneling

Owing to the large mobility of the superfluid-solid interface, crystallization of solid 4He is not limited by
dissipation processes and, therefore, this system provides a good model for studies of MQT. We have made
a detailed study on the formation of solid from the superfluid phase at the temperature range 2 mK–1.0 K
[PRL 77, 2514 (1996)].
 
Statistical nucleation event distri-butions in overpressure (see FIG. on the left) were found to be broad, asymmetric, and temper- ature independent below 100 mK; solid formation took place at pressures much below the values of quantum nucleation predicted for bulk solidification by Lifshitz and Kagan. 

Our statistical analysis agrees with a theoretical model suggesting that solid formation is driven by macroscopic quantum mechan- ical fluctuations from a seed preexisting in a cavity on the wall.
 

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