Third sound in He-3-He-4 films: The He-3 low-coverage limit

The preliminary results of a calculation of the variation of third sound velocity as a function of the concentration of He-3 in superfluid He-4 films on a Nuclepore substrate are presented and compared with experimental data. The He-3 atoms in the transverse ground-state are treated as a normal fluid blanket on top of the superfluid film. The measured third sound speeds can only be understood by assuming that the He-3 submonolayer film has a minimum thickness which is approximately equal to the quantum mechanical size of the atom.