Theory of the time evolution of exciton coherence in weakly disordered crystals

Abstract

Coherent states in molecular crystals are described as minimum-uncertainty superpositions of all the crystal states that can interact with light, and their amplitude decay due to the presence of disorder is calculated through the time-dependent exciton Greens function. The functional form of the decay is investigated, and different methods for its calculation are compared. The decay obtainable for the k=0 vibrational exciton in α-N2 through direct time-domain approximations provides good agreement with experimental results.