Propagation of surface sound in superfluid He3 - He4

"Surface sound," a longitudinal compressional wave in He3 adsorbed on the surface of superfluid He4, has been propagated in the temperature range from 20 to 120 mK. Measurements of the surface-sound velocity and of the surface tension are compared to a model of interacting surface He3 quasiparticles. A least-squares fit to the model is used to obtain the He3 binding energy, ε0kB=2.28±0.03 K, the He3 effective mass, Mm3=1.3±0.1, and some limits on the sign and magnitude of the effective interaction between the quasiparticles. The interaction is found to be very weak and predominantly repulsive at large distances.