In-plane optical anisotropy for the charge/orbital ordered state in half-doped layered manganites

Abstract

We have investigated the in-plane anisotropy of the electronic response for the charge/orbital ordering (CO–OO) phase in half-doped layered manganites. It has been suggested that the CE-type magnetically ordered CO–OO phase might show the electronic anisotropy in the MnO 2 plane due to the quasi-one-dimensional electron hopping along the ferromagnetic chain. To address this issue, we measured optical spectra for a single domain of layered manganites Eu 1/2Ca 3/2MnO 4 with polarization dependence. It was found that the optical conductivity along the chain direction exhibits smaller optical gap and lower energy distribution of the spectral weight than along the stripe (interchain) direction. This sizable anisotropy, which is identified below the CO–OO transition temperature, is attributed mainly to the e g orbital ordering.