Elementary excitation spectrum and heat capacity of He-4 monolayers adsorbed on evaporated gold

Using the temperature-dependent elementary excitation of liquid He-4 films derived within the chain-diagram approximation, the heat capacity data of H e-4 films adsorbed on an evaporated gold substrate are successfully fitted for coverages between 0.007 and 0.096 Angstrom (-2) and temperatures betwee n 0.4 and 2.5 K. In the long-wavelength limit, the spectra deduced from the data are anomalous and the upward bending becomes stronger as the density increases. With increasing density, the sound and roton energy gap increase respectively, while the roton energy gap decreases with increasing tempera ture. This reduction becomes larger as the coverage decreases. In general, the elementary excitation spectra deduced from the specific heat data are v ery similar to those of bulk liquid He-4.