Infrared response of ordered polarons in layered perovskites

We report on the infrared absorption spectra of three oxides, were charged superlattices have been recently observed in diffraction experiments. In La1.67Sr0.33NiO4, polaron localization is found to suppress the low-energy conductivity through the opening of a gap and to split the E(2u)-A(2u) vibrational manifold of the oxygen octahedra. Similar effects are detected in Sr1.5La0.5MnO4 and in La2NiO4+y with peculiar differences related to the type of charge ordering.