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Bar plot of the percentage of phonons on each of the six phonon branches that are produced by the anharmonic decay of g-type LO phonons. Most gLO phonons decay into combinations of and some phonons, while very few decays result in both phonons on the same branch. The decay channel is dominant, in agreement with previous calculations.
Energy distribution plot of the number of phonons produced by the anharmonic decay of g-type longitudinal optical (gLO) phonons vs their energy. Most phonons break up into one low energy acoustic and one higher energy longitudinal phonon. This can be seen from the energy distribution having two peaks: One around 25 meV belonging to the TA branch, and one around 45 meV either on the acoustic or optical longitudinal branch. The equilibrium phonon distribution (dashed line) shows that only lower energy (below 25 meV) phonons belonging to the transverse acoustic branch are near equilibrium, while the LA phonons are nonequilibrium.
Phonons produced by the decay of gLO phonons are simulated further and many of them undergo a second decay, producing yet another phonon. The distribution of such phonon vs their energies is plotted here showing that the second anharmonic decay process removes the peak that was previously present between 40 and 50 meV. This distribution closely matches the equilibrium distribution (dashed line), thereby demonstrating that only this second anharmonic decay returns all phonons fully to equilibrium. This implies that slow intervalley optical phonons require additional time to fully decay back to faster equilibrium TA phonons.
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