We investigated the electronic structures of the two-dimensional layered perovskite Sr2\textit{M}O4 (\textit{M}=4\textit{d} Ru, 4\textit{d} Rh, and 5\textit{d} Ir) using optical spectroscopy and polarization-dependent O 1\textit{s} 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 4\textit{d} and 5\textit{d} layered oxides. The energy splittings between the two eg orbitals, i.e., d3z2−r2 and dx2−y2, are about 2 eV, which is much larger than those in the pseudocubic and 3\textit{d} layered perovskite oxides. The electronic properties of the Sr2\textit{M}O4 compounds are discussed in terms of the crystal structure and the extended character of the 4\textit{d} and 5\textit{d} orbitals.
@article{arxiv.cond-mat/0607026,
title = {Electronic structures of layered perovskite Sr2MO4 (M=Ru, Rh, and Ir)},
author = {S. J. Moon and M. W. Kim and K. W. Kim and Y. S. Lee and J. -Y. Kim and J. -H. Park and B. J. Kim and S. -J. Oh and S. Nakatsuji and Y. Maeno and I. Nagai and S. I. Ikeda and G. Cao and T. W. Noh},
journal= {arXiv preprint arXiv:cond-mat/0607026},
year = {2009}
}