HIGH-RESOLUTION OXYGEN-K ABSORPTION STUDY OF BI2SR2CA1-XYXCU2O8 (X=0.0 AND 0.6) AND YBA2CU2O7-DELTA (DELTA=0.0-0.7)

High-energy-resolved oxygen K absorption spectra of Bi2Sr2Ca1-xYxCu2O8 (x = 0.0 and 0.6) single crystals and YBa2Cu3O7-delta (delta = 0.0-0.7) ceramics were reported. The experimental results show that (1) the electronic states at the Fermi level in superconductor has a dominant O2px,y symmetry, (2) the lowest unoccupied states in nonsuperconductor is located about 1 eV above the Fermi level and also has a strong in-plane symmetry, and (3) hole-doping causes a transfer of weight of the electronic states from the lowest unoccupied states (upper Hubbard band) to the mid-gap states produced by hole-doping at the Fermi level.