Critical Velocity of Superfluid Helium Films

Abstract

Superfluidity in systems of restricted geometry has recently been investigated intensively, in particular, by experiments. The Californian group has been doing a series of experiments on third sound in superfluid helium films and found out many interesting facts such as the onset film thickness of superfluidity, depending on temperature, the existence of finite superfluid density at the onsetu •2) and the observation of the maximum of superfluid critical velocity, depending on the film thickness. 'l It has been established that near the lambda point there exists only one characteristic length called healing length ~ theoretically') as well as experimentally. 5l On this basis we may expect the superfluid critical velocity Vsc to be given as a function of the film thickness d by