Superfluid dissipation in thin films of ⁴He adsorbed on graphite

We have completed a torsional oscillator study of superfluidity in thin films of ⁴He adsorbed on the basal plane of graphite for coverages above one atomic layer. In this report we focus on the details of the superfluid dissipation. For coverages above 2 1 4 layers we resolve a dissipation peak at the superfluid transition. The evolution of this peak with increasing coverage is distinct from the behavior observed on heterogeneous substrates such as mylar. In particular, we observe two coverage regions, in the third and fourth layers, where the temperature of the dissipation maximum is nearly independent of the coverage.