Phonon damping of excitons in cryocrystals of inert elements
Abstract
The damping Γk(T) and nonadiabtic displacement of excitonic states in cryocrystals of inert elements with single phonon scattering are studied over a wide range of temperatures and values of exciton quasi-momenta. A detailed analysis of the different limiting situations (with respect to temperature and magnitude of the quasimomentum) is carried out and calculations of the damping of the exciton states are presented in analytic form. For purposes of practical application and checking the applicability of the theoretical approximations, the results of an exact numerical calculation of Γk(T) are examined. It is shown that excitons remain “good” quasiparticles only for temperatures that do not exceed a critical value Tc and quasimomenta that are greater than some limiting values k0 (T). The nature of the change in damping as a function of the magnitude of the exciton wave vector is analyzed in detail. It is established that taking into account nonadiabatic exciton-phonon interactions lowers the exciton states by several Debye frequencies.