Superflow in Solid 4He

Abstract

Kim and Chan have recently observed Non-Classical Rotational Inertia (NCRI) for solid ${}^4$He in Vycor glass, gold film, and bulk. Their low $T$ value of the superfluid fraction, ${\rho }_s/\rho \approx 0.015$, is consistent with what is known of the atomic delocalization in this quantum solid. By including a lattice mass density ${\rho }_L$ distinct from the normal fluid density ${\rho }_n$, we argue that ${\rho }_s(T)\approx {\rho }_s(0)-{\rho }_n(T)$, and we develop a model for the normal fluid density ${\rho }_n$ with contributions from longitudinal phonons and ``defectons'' (which dominate). The Bose-Einstein Condensation (BEC) and macroscopic phase inferred from NCRI implies quantum vortex lines and quantum vortex rings, which may explain the unusually low critical velocity and certain hysteretic phenomena.

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