Spontaneous decay of TA phonons

Abstract
Anharmonic decay of high-energy transverse acoustic (TA) phonons satisfying ħω≫kBT is studied taking account of the elastic anisotropy of real crystalline solids. Dispersive effects are assumed to be small. We find that the decay rate is very anisotropic. The possibility of observing this anisotropy in a phonon-focusing experiment is discussed.