Microscopic theory of anisotropic organic cavity exciton polaritons

Abstract

We consider crystalline organic microcavities in the strong coupling regime. Using a microscopic theory to describe the Frenkel excitons and their coupling to the cavity photon modes, we derive the cavity exciton-polariton dispersion relations and quantum states, for the two cases of anisotropic organic crystals with one and two molecules per unit cell. In the most general case, the cavity exciton polaritons are a coherent superposition of both Davydov exciton branches and of both cavity mode polarizations. The polarization mixing, which occurs also in the case of a single molecule per unit cell, is in contrast to the case of typical inorganic semiconductor cavities in which TM and TE polarizations do not mix. We derive the transmission, reflection, and absorption coefficients for organic cavities by applying the quasimode approximation for high quality cavities. The crossed polarized spectra, e.g., the TM polarized reflected light for TE polarized incident light, clearly show the optical anisotropy of organic microcavities in the regime of strong coupling.