Superfluidity in Finite Systems: Propagation of Fourth Sound and the Density of Superfluid

Measurements have been made of the fractional density of superfluid, $\frac{{\rho }_s}{\rho }$, in helium II contained in micropores (average radius ∼31 Å), as calculated from fourth-sound measurements between 1.2 and 2°K. Since the lambda transition is greatly modified in this system, the temperature variation of $\frac{{\rho }_s}{\rho }$ may generally be expected to differ from that in "infinite" bulk liquid, at least near the transition temperature. The results lead to the conclusion that the critical velocity in such channels decreases rapidly with increasing temperature above 1.2°K.