High-frequency phonon transmission between a solid and superfluid4He

Abstract

The frequency dependence of phonon transmission through a solid-liquid ⁴He interface is studied on the basis of a simple model of the solid-liquid coupling. For single-quantum processes the transmission coefficient is calculated using a T-matrix formalism and shows extremely sharp peaks, where the transmission probability becomes unity, at frequencies near the roton minimum and phonon maximum of the superfluid dispersion curve. Multi excitation processes in the helium are also analysed but are found to be small. The conditions required for observation of transmission peaks are discussed with reference to recent experimental data on high-frequency phonon transmission and modifications of the model are proposed.