Superfluidity and Heat Transport in the Unsaturated Helium-II Film

Abstract

The mobility of unsaturated He-II films has been investigated by heat transport measurements as a function of thickness and temperature. The results confirm data from previous flow measurements that at a given temperature a certain number of layers are immobile, changing smoothly from ∼2 at 1.3°K to ∼10.5 at 2.0°K. All additional layers flow in a temperature gradient with about the same drift velocity, this velocity being of the same order of magnitude as that derived from the transfer rate of the saturated film. Films of thickness between 20-80 layers show superfluidity at and even slightly above the $\lambda$ temperature of the bulk liquid.