PHOTOEMISSION AND ELECTRONIC-STRUCTURE STUDIES OF YBA2CU3OX

High-resolution angle-resolved photoelectron spectroscopy measurements are reported for YBa2Cu3Ox when the oxygen stoichiometry x is varied between 6.9 (92 K superconductor) and 6.2 (insulator). Fermi surfaces obtained from energy distribution curve measurements on a grid scanning the entire first Brillouin zone are reported for the x = 6.9 sample. Bands along the GAMMA-S symmetry line were measured for samples with reduced oxygen stoichiometry. For superconducting samples, these bands are essentially independent of x. As the material becomes insulating (x < 6.4), a dramatic falloff of spectral weight near E(F) is observed. Resonant spectral features also disappear. Efforts to observe a superconducting gap are reported.