Interplay of exciton or electron transfer and relaxation

Abstract

Mori theory together with canonical transformation but with quantities of interest remaining untransformed is applied to the exciton- or electron-phonon system with site-diagonal linear coupling and full exciton or electron density matrix; finite concentrations of the carriers are admitted. Partial small polaron transformation is used which allows to investigate relaxation of initially relaxed systems without initial-condition terms. The result is applied, in the lowest order in the coupling, to a particle on a symmetric dimer. Coefficients suggested in a recent generalization of the Haken-Strobl-Reineker model are identified. The theory surprisingly, is found to be, in the above order, insufficient to yield a loss of coherence of carrier propagation with increasing time, though standard Markovian treatment suggests the opposite. A new type of a so far unnoticed drawback, typical of finite-order time-convulution theories, which is connected with the infinite memory of the initial lattice relaxation becomes conspicuous.