Interface between Superfluid and SolidHe4

Abstract

With an optical technique it is found that the equilibrium interface between superfluid and hcp ${}_{}{}^4{}_{}{}^{}\mathrm{He}$ is partially faceted, showing that at least some of it is atomically smooth. This conclusion is also consistent with the behavior of the crystal during melting and growth. The surface tension ${\alpha }_{\mathrm{LS}}$ on the rounded part of the interface is found to be independent of temperature.