Spin-orbital physics in the optical conductivity of quarter-filled manganites

Abstract

Using finite-temperature diagonalization we investigate the optical conductivity $\ensuremath{\sigma}(\ensuremath{\omega})$ and spin-orbital dynamics in the CE phase of half-doped manganites. We find $\ensuremath{\sigma}(\ensuremath{\omega})$ characterized by a broad spectrum with pronounced optical gap due to charge ordering induced by Coulomb and further-neighbor Jahn-Teller interactions. With increasing temperature the conductivity shows a significant change over a wide energy range with a characteristic shift towards lower frequencies. In the low-temperature CE phase we observe in-gap absorption due to combined orbiton-spin excitations.