Slippage of 4He films adsorbed on porous gold

We measured the slippage of nonsuperfluid 4He films adsorbed on a porous gold substrate using the quartz-crystal microbalance (QCM) technique. The substrate has a highly uniform porous structure, and its effective surface area was 20 times larger than that of a flat substrate. It was found that the degree of slippage between 4He films and the substrate increases below a certain temperature TS, and that TS decreases with increasing 4He areal density. This increase depends strongly on the oscillating amplitude of the quartz crystal.