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

We present a calculation of the third sound speed C3 of thin He-4 film s adsorbed on H-2, Li, Mg, graphite and H-2-plated graphite. The resul ts show a clear correlation of oscillations in C3, with a period of on e atomic layer, with the layering phenomena observed in adsorption iso therms. Comparison is made with recent experimental results for helium films on solid H-2 by Shirron and Mochel and by Brisson, Mester and S ilvera. The theoretical analysis suggests explanations for disagreemen ts between different interpretations of data. A standard way of determ ining the number of so-called inert layers is questioned. Other availa ble experimental data on graphite and H-2-plated graphite are also dis cussed.