Solidification and Superfluidity ofHe4in Porous Vycor Glass

Abstract
The onset of solidification of He4 in porous Vycor is identified from changes in transverse sound velocity. From observed overpressures required to initiate freezing (ranging from 18 bars at 1.3 K to 30.7 bars at 2.38 K), the interfacial energy between liquid and solid He4 was estimated. The superfluid transition up to 35.5 bars was also observed.