Propagation of surface sound in superfluidHe3-He4

Abstract

"Surface sound," a longitudinal compressional wave in ${}_{}{}^3{}_{}{}^{}\mathrm{He}$ adsorbed on the surface of superfluid ${}_{}{}^4{}_{}{}^{}\mathrm{He}$, 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 ${}_{}{}^3{}_{}{}^{}\mathrm{He}$ quasiparticles. A least-squares fit to the model is used to obtain the ${}_{}{}^3{}_{}{}^{}\mathrm{He}$ binding energy, $\frac{{\epsilon }_0}{k_B}=2.28\mathrm{}\pm 0.03$ K, the ${}_{}{}^3{}_{}{}^{}\mathrm{He}$ effective mass, $\frac{M}{m_3}=1.3\mathrm{}\pm 0.1$, 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.