ELECTRONIC-STRUCTURE OF BI-BASED COPPER-OXIDE SUPERCONDUCTORS - A COMPARATIVE PHOTOEMISSION-STUDY OF BI2SR2CACU2O8, BI2SR2CUO6, AND BI2SR2COO6+DELTA

Bi-based high-Tc copper oxide superconductors, Bi2Sr2CaCu2O8, Bi2Sr2CuO6, and a related material Bi2Sr2CoO6+ have been studied by photoemission spectroscopy. While common prominent structures at high-binding energies (>2 eV) are attributed to oxygen 2p states in the Bi-O planes, emission near the Fermi level (EF) is different from one other, indicating that these states are oxygen 2p states hybridizing with the transition-metal 3d states. For the states near EF, the resonant behavior at the Cu 3p-3d absorption threshold and the photon energy dependence of the intensities are shown to be consistent with CuO3d9O 2p hole local singlets formed within the CuO2 planes. © 1990 The American Physical Society.