THEORETICAL-STUDY OF 3RD SOUND IN A LAYERED SUPERFLUID FILM

We present a calculation of the third sound speed C3 of thin He-4 films adsorbed on H-2, Li, Mg, graphite and H-2-plated graphite. The results show a clear correlation of oscillations in C3, with a period of one atomic layer, with the layering phenomena observed in adsorption isotherms. Comparison is made with recent experimental results for helium films on solid H-2 by Shirron and Mochel and by Brisson, Mester and Silvera. The theoretical analysis suggests explanations for disagreements between different interpretations of data. A standard way of determining the number of so-called inert layers is questioned. Other available experimental data on graphite and H-2-plated graphite are also discussed.