High-resolution oxygen-K absorption study of Bi2Sr2Ca1−xYxCu2O8 (x=0.0 and 0.6) and YBa2Cu2O7−δ (δ=0.0−0.7)

High-energy-resolved oxygen K absorption spectra of Bi2Sr2Ca1−xYxCu2O8 (x=0.0 and 0.6) single crystals and YBa2Cu3O7−δ ( δ =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 O2p x,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.