Anisotropy of longitudinal ultrasonic absorption in anharmonic processes of scattering in Ge, Si, InSb, MgO, and KCl cubic crystals: The role of damping of phonon states

The relaxation of longitudinal phonons and absorption of ultrasound in cubic crystals with positive (Ge, Si, InSb, MgO) and negative (KCl) anisotropies of the second-order elastic moduli have been investigated. The scattering processes occurring with the participation of three longitudinal phonons (the LLL mechanism) and the processes of scattering of a longitudinal phonon by two transverse thermal phonons (the LTT mechanism) have been considered in terms of the anisotropic-continuum model. The influence of damping of phonon states on the anisotropy of longitudinal ultrasonic absorption has been examined. The specific features of phonon scattering and the influence of anisotropy of the harmonic and anharmonic energies of the cubic crystals on the ultrasonic absorption have been analyzed. In contrast to the previously performed calculations, the influence of cubic anisotropy of the harmonic and anharmonic energies of the phonon system on the relaxation processes has been exactly taken into account in the present study. The results of the calculations have been compared with experimental data.