Resonant absorption of sound by surface of copper single crystal
Zinov'eva K. N. , Karstens G. E. , Kashlyuk A. V. , Semenov A. S.
The passage of acoustic phonons from liquid 4He into an anisotropic copper single crystal has been studied experimentally for the first time in the temperature interval 100-400 mK and in the frequency interval 13-91 MHz. The angular dependence of the coefficient of the transmission of phonon energy into the crystal has been studied. Sharp peaks have been found in this transmission coefficient in the case of the (001) basal plane of the crystal and the (100) plane of incidence of the sound at an angle of incidence equal to the critical angle θκ. The width of these peaks is δ ~ 5-10', and their height is a ss 0.1. A significant increase in the transmission coefficient for ballistic phonons at angles near normal incidence has been observed for the first time. It is explained.