Electronic structures of layered perovskite Sr2 M O4 (M=Ru, Rh, and Ir)

We investigated the electronic structures of the two-dimensional layered perovskite Sr2 M O4 (M=4d Ru, 4d Rh, and 5d Ir) using optical spectroscopy and polarization-dependent O 1s x-ray absorption spectroscopy. While the ground states of the series of compounds are rather different, their optical conductivity spectra σ (ω) exhibit similar interband transitions, indicative of the common electronic structures of the 4d and 5d layered oxides. The energy splittings between the two eg orbitals, i.e., d3 z2 - r2 and d x2 - y2, are about 2 eV, which is much larger than those in the pseudocubic and 3d layered perovskite oxides. The electronic properties of the Sr2 M O4 compounds are discussed in terms of the crystal structure and the extended character of the 4d and 5d orbitals.