Two-dimensional plasmons (2DP) and acoustic waves in crystals

The interaction of 2DP with elastic waves in crystals opens up new interesting possibilities to control the wave processes in solids. The present paper deals with the coupled plasma-acoustic oscillations on the surface of crystals. The coupling takes place between the shear surface or bulk waves and the longitudinal waves in a plasma sheet. Such an interaction could be realized in the inversion layer of the MOS structures or in a thin film of a semimetal or a doped semiconductor deposited on the surface of a crystal, or at last for electrons over a film of liquid helium lying on a crystal substrate. The plasmons can generate both bulk and surface hypersound waves. The coupling between plasma and acoustic waves by means of piezoeffect and deformation potential is considered.