SUPERFLUIDITY OF ATOMICALLY LAYERED HE-4 FILMS

The superfluidity of He-4 films adsorbed on the atomically flat surfac e of graphite, preplated with KD to tune the surface binding potential , has been studied using a torsional oscillator. The superfluidity of a single uniform fluid layer of He-4 shows an intrinsic coverage depen dent suppression, while the fluid bilayer is fully superfluid at T = 0 . The contribution of nonvortex excitations in the film to the normal density shows a strong dependence on coverage, arising from the atomic layering of the film.