New coupling mechanism of high frequency phonons at interfaces

Experiments with solids coated by oxide, metal or He films — or simply by not specified dirt — show diffuse and inelastic scattering at such interfaces for phonons above 10¹⁰ Hz. A new interaction mechanism is proposed enhancing the diffuse scattering at coated surfaces. This mechanism is due to charges in the coating pinned to the interface, so that their relative motion under impinging phonons generates rf fields, which then act back on the charges.