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Categoria: Appuntamenti

Delocalization and trapping of incoherent excitations in a disordered medium

Seminario del Prof. Stanislav Fedorenko giovedì 16 gennaio ore 15:00 - Aula "A. Rostagni" (Fisica)

Giovedí 16 gennaio 2020, alle ore 15:00 in Aula "A. Rostagni" (Fisica) il Prof. Stanislav Fedorenko del V.V. Voevodsky Institute of Chemical Kinetics and Combustion of the Siberian Branch of the Russian Academy of Sciences, Russia, terrà il seminario

"Delocalization and trapping of incoherent excitations in a disordered medium"


We consider the kinetic aspects of relaxation of incohe rent carriers of energy and charge in disordered systems. In an incoherent description, transitions in microscopic pairs donor-donor and donor-trap occur at a constant rate, quadratic in interaction. This rate is a function of the distance in the pair and the activation factor, which depends on the system of energy levels of the interacting pair. On the whole, at this stage, the macroscopic system is described by a system of Master Equations giving a universal description of such seemingly different processes as the electron energy transfer in crystals and glasses, the spin excitations transfer in solutions of paramagnetic particles, the localized charge carriers capture to traps in disordered systems, etc. The most informative characteristic of all these processes is kinetics (survival probability of excitation/carier), which depends both on the type and magnitude of microscopic interactions, and on the dimensionality of the space and the concentration of impurities, donors and traps, randomly distributed in the system. The way in which the observed kinetics functionally depends on all these parameters is called the kinetic mechanism of carrier relaxation in traps. The theory allows us to identify three basic mechanisms of carrier relaxation in a disordered system: static, migration-accelerated, and fluctuation one, and to calculate the kinetics for each of these cases. The identification of the kinetic mechanism in the experimentally studied kinetics uniquely determines the “scenario” of the physical processes occurring in a given measurement interval, provides information on the structure of the system and the types of interactions that are realized in the process of carrier migration and relaxation. The subsequent direct fitting allows us to finalize the values of all control parameters of carrier relaxation in the disordered system under study.