THE EXCITON POLARITON - MICROSCOPIC DERIVATION OF THE PHENOMENOLOGICAL THEORY

From a microscopic model including all excitonic levels, we derive the exciton-polariton dispersion spectrum. Our results, which differ from previous microscopic calculations, justify the phenomenological theory in which only the lowest exciton level is considered. We show how the higher levels generate the phenomenological "high frequency dielectric constant" which not only modifies the photon velocity at q approximately 0, but also reduces the exciton-photon coupling.