The doping and temperature dependent optical conductivity spectra of the quasi-two-dimensional Ca_{2-x}Sr_xRuO_4 (0.0=<x=<2.0) system were investigated. In the Mott insulating state, two electron correlation-induced peaks were observed around 1.0 and 1.9 eV, which could be understood in terms of the 3-orbital Hubbard model. The low frequency peak showed a shift toward higher frequency as temperature was lowered, which indicated that electron-phonon interactions play an important role in the orbital arrangements. From the systematic analysis, it was suggested that the antiferro-orbital and the ferro-orbital ordering states could coexist.
@article{arxiv.cond-mat/0208075,
title = {Electron and orbital correlations in Ca_{2-x}Sr_{x}RuO_{4} probed by optical spectroscopy},
author = {J. S. Lee and Y. S. Lee and T. W. Noh and S. -J. Oh and Jaejun Yu and S. Nakatsuji and H. Fukazawa and Y. Maeno},
journal= {arXiv preprint arXiv:cond-mat/0208075},
year = {2009}
}