Relaxation Theory Applied to Scattering of Excitations and Optical Transitions in Crystals and Solids

Abstract

In this chapter, we will discuss the application of standard quantum relaxation theory to the problems of excitation transport and scattering in molecular solids and dephasing of optical transitions in solids and glasses, all at low temperatures. In the next section, we will review the standard theory based on the weak coupling approximation (Redfield theory), and apply a number of simple microscopic models to discuss the dynamics and temperature dependence of various processes. In the third section we apply these ideas to the study of the scattering of delocalized excitations in low-temperature solids, including the effects of impurities to low order. We compare our theoretical results to the experimental results of Schmidt (this volume). In the fourth section, we discuss the homogeneous optical line shapes of localized excitations in crystals and glasses, presenting a number of the dynamical models used to discuss this phenomenon. The many models used to describe the dephasing of the optical transition are compared and it is shown how to derive the results of these models from the standard Redfield theory. Unfortunately, because many of the microscopic parameters are unknown, it is not yet possible to decide which is the correct model. This is discussed in detail in Section 4.KeywordsOptical TransitionOptical CenterDensity Matrix ElementRelaxation TheoryPure DephasingThese keywords were added by machine and not by the authors. This process is experimental and the keywords may be updated as the learning algorithm improves.