Electronic structure of high-Tc superconductors studied using photoelectron spectroscopy

Fundamental information about the structure of the valence band and the chemical valence states of the various constituents of the LaSrCu, YBaCu, BiSrCaCu and TlCaBaCu oxides have been obtained using photoelectron spectroscopy. These results show that the one-electron theories do not adequately describe the electronic structure of these superconductors. The atomic origins of the features observed in the valence bands have been investigated by studying photoemission resonances and changes in excitation cross-sections with photon energy. Results to date suggest that these materials have varying densities of states at the Fermi level, valence bands composed of O 2p and Cu 3d states, and display no significant changes in the band structure associated with the superconducting behaviour when the temperature is lowered below Tc. In addition, the complex surface chemistry of these oxides make it essential to study the surface stoichiometry and the interaction of simple molecules. O2 and CO are found to interact only weakly with the surfaces of the materials studied to date, while the H2O and CO2 react strongly, forming hydroxides and carbonates. © 1989