Optical investigation of the electronic structures of Y2Ru2O7, CaRuO3, SrRuO3, and Bi2Ru2O7 -: art. no. 245107

We investigated the electronic structures of the bandwidth-controlled ruthenates, Y2Ru2O7, CaRuO3, SrRuO3, and Bi2Ru2O7, by optical conductivity analysis in a wide energy region of 5 meV-12 eV. We could assign optical transitions from the systematic changes of the spectra and by comparison with the O 1s x-ray absorption data. We estimated some physical parameters, such as the on-site Coulomb repulsion energy and the crystal-field splitting energy. These parameters show that the 4d orbitals should be more extended than 3d ones. These results are also discussed in terms of the Mott-Hubbard model.