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 ${\mathrm{La}}_{1.67}$ ${\mathrm{Sr}}_{0.33}$Ni${\mathrm{O}}_4$, 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 ${\mathrm{Sr}}_{1.5}$ ${\mathrm{La}}_{0.5}$Mn${\mathrm{O}}_4$ and in ${\mathrm{La}}_2\mathrm{Ni}{\mathrm{O}}_{4+y}$, with peculiar differences related to the type of charge ordering.