Exciton-Phonon Interactions

Abstract

Phonons are very important in solid state physics because they are the intrinsic characters of any solid in any form, and they are involved in most excitonic reactions. For instance, the formation of an exciton from an excited free electron and hole pair or vice versa is not possible in a crystal without the involvement of phonons to conserve the energy and momentum. There are two types of phonons: optical and acoustic. The optical phonons have higher frequencies (in the optical to infrared regions) and acoustic phonons have lower frequencies. The frequency of optical phonons is nearly independent of phonon wavevectors, while that of acoustic phonons increases with phonon wavevectors starting from zero to a saturation limit. There are several books^(1–4) and articles^(5–7) available on phonons and so we will present here only a brief comparative study of the interaction energy operator of Wannier excitons and phonons and Frenkel excitons and phonons derived from various types of electron-phonon interactions.