Infrared response of ordered polarons in layered perovskites.

We report on the infrared absorption spectra of three oxides, where charged superlattices have been recently observed in diffraction experiments. In La{sub 1.67}Sr{sub 0.33}NiO{sub 4}, polaron localization is found to suppress the low-energy conductivity through the opening of a gap and to split the {ital E}{sub 2{ital u}}-{ital A}{sub 2{ital u}} vibrational manifold of the oxygen octahedra. Similar effects are detected in Sr{sub 1.5}La{sub 0.5}MnO{sub 4} and in La{sub 2}NiO{sub 4+{ital y}}, with peculiar differences related to the type of charge ordering. {copyright} {ital 1996 The American Physical Society.}