Nonequilibrium phonon dynamics beyond the quasiequilibrium approach

摘要

The description of nonequilibrium states of solids in a simplified manner isa challenge in the field of ultrafast dynamics. Here, the phonon thermalizationin solids through the three-phonon scatterings is investigated by solving theBoltzmann transport equation (BTE). The numerical solution of the BTE showsthat the transverse acoustic and longitudinal acoustic (LA) phonon temperaturesare not well-defined during the relaxation, indicating the breakdown of thequasiequilibrium approximation. The development of hot and cold phonons and thebackward energy flow from low to high energy phonons are observed in theinitial and final stage of the relaxation, respectively. A minimal model ispresented to relate the latter with the power-law decay of the LA phononenergy.