Interaction of Rydberg excitons in cuprous oxide with phonons and photons: optical linewidth and polariton effect

We demonstrate that the optical linewidth of Rydberg excitons in Cu₂O can be completely explained by scattering with acoustical and optical phonons, whereby the dominant contributions stems from the non-polar optical ${\Gamma }_3^{-}$ and ${\Gamma }_5^{-}$ modes. The consequences for the observation of polariton effects are discussed. We find that an anti-crossing of photon and exciton dispersions exists only for states with main quantum numbers n > 28, so polariton effects do not play any role in the experiments reported up to now. (paper)