Phonon propagation with isotope scattering and spontaneous anharmonic decay

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Abstract
Calculations of the propagation of high-energy phonons introduced into a crystal at T=0 K are presented. The phonons are assumed to undergo elastic scattering and anharmonic decay processes. We show that in addition to the ‘‘quasidiffusion’’ component to the phonon propagation (discussed previously by Levinson and co-workers) there is also a contribution that arrives at close to the time expected for ballistic propagation. This latter mode of propagation continues to be of substantial importance even when the elastic scattering is much stronger than the anharmonic processes.