Introduction to an analysis of kinematical exciton levels

Abstract

The possibility of the existence of kinematical levels for a multi-level exciton scheme is analysed and it is shown that such levels exist for all the values of the wave vector. This is the consequence of the fact that the exciton gap is much larger than the energy bandwidth. The existence of kinematical levels is proved using a more correct method of decoupling of higher order Green's functions in which pairing is performed not only for the same moments of time but for different moments as well. A matrix formulation of the system of equations for Green's function is proposed and the analysis is performed in this condensed form representing a sensible simplification which could be helpful for the analysis of other multilevel excitation systems, too. © 1978.