Localization of Cu 3D Levels in the High Tc Superconductor YBa2Cu3O Approximately 7 by Cu 2p X-ray Photoelectron Spectroscopy

摘要

The copper 2p(1/2) and 2p(3/2) X-ray photoelectron core level spectra (XPS) of the single phase high temperature (Tc=91 K) superconductor YBa2Cu3O approximately 7 were measured. Evidence for the strong localization of valence Cu 3d electrons is indicated by the Coulomb interaction U(cd)=9 eV between the 2p(3/2) core hole and the localized 3d valence electron. A Coulomb interaction U(dd) of the order of 6 eV between 3d valence electrons is estimated. No evidence of the 2p3d(8) final state due to the Cu(3+) ions is found. The broadening of atomic multiplets of the final state 2p3d(9) going from CuO to YBa2Cu3O approximately 7 is observed. The results are consistent with the formation of holes L in the oxygen derived band, i.e., of the 3d(9) L configuration, with additional oxygen x in YBa2Cu3O(6.5+x) which should play a key role in the high-Tc superconductivity.