Electronic correlations and satellites in superconducting oxides

The satellite observed at binding energy of 12--13 eV below the Fermi level in the high-T/sub c/ oxide superconductors La/sub 2-//sub x/Sr/sub x/CuO4 and YBa2Cu3O/sub 7-//sub δ/ is viewed as originating from a state with two holes bound at the same Cu site. As in the case of Ni metal, the satellite is caused by an intra-d-shell shakeup process into a Cu 3d8 final state and its intensity is enhanced at resonance because of a super-Koster-Kronig transition. Based on the t-matrix approach for the hole self-energy, we study the effect of electronic correlations on the one-electron band structure. We examine the position of the satellite and find a large Coulomb interaction energy of ∼5 eV at the Cu site when the experimental satellite position is duplicated by the theory. Since this energy is comparable with the 3d bandwidth, the two-hole bound state is a high-energy excitation. This indicates that in the ground state a creation of two holes at the Cu site is unlikely and thus holes are formed at the O sites when Sr is substituted for La in La2CuO4 and when the oxidation is increased in YBa2Cu3O/sub 7-//sub δ/