Frequency and Temperature Dependence of Anharmonicity-Induced Multiphonon Absorption

Abstract

First-principles calculations of the frequency and temperature dependence of multiphonon absorption in crystals, due to anharmonicity, are carried out within the formalism of Bendow, Ying, and Yukon, employing various simplified phonon models. The frequency dependence of the absorption coefficient α is found to be exponential-like in all cases, in agreement with previous predictions. It is found that the temperature dependence of $\alpha$ is not determined by explicit temperature variations alone, but by the temperature dependence of the phonon spectrum as well. The latter effect leads to a strong suppression of the temperature dependence of $\alpha$ in ionic crystals. Over-all agreement of the present predictions with experimental data demonstrates that the present approach accounts successfully for the principal properties displayed in multiphonon absorption in crystals.