Ultrafast radiative decay of polaritons in an interface layer with strong excitonic response

We have demonstrated theoretically that radiative polaritons in an interface layer having strong excitonic response exhibit appreciable frequency dependence on an in-plane wave vector, k∥, in the region of the ω-k∥ dispersion plane between the “light-lines” of the media to either side of the layer. We predict ultrafast radiative decay of such polaritons with lifetimes as low as 10 fs in slabs of organic-inorganic PbI-based layered perovskite-type semiconductors. We confirm an unusual physical feature of the radiative polaritons by determining the linear electromagnetic response of the excitonic layer to a current δ-pulse.