The O 2p holes in the Cu- and Bi-based oxide superconductors La-Sr-Cu-O, Y-Ba-Cu-O, Bi-Sr-Ca-Cu-O, Tl-Ba-Ca-Cu-O, and Ba-K-Bi-O, and in CuO have been investigated with inverse photoelectron spectroscopy. These states exhibit a unique resonance for incident electron energies near the O 2s shallow core in the Cu-based superconductors but it is not observed in CuO or in Ba-K-Bi-O. Variations in the resonance show that the number of O 2p holes (1) increases at 60 K compared to 300 K, (2) is significantly reduced in oxygen-deficient samples, (3) is altered but not quenched upon Pr substitution for Y, (4) is reduced by electron bombardment at ∼1500 eV, and (5) is quenched by Cu- or Au-adatom-induced surface disruption. The Bi-Sr-Ca-Cu-O surfaces are found to be the most stable against high-energy electron bombardment and interface formation.

• Received 15 September 1989

DOI:https://doi.org/10.1103/PhysRevB.41.4201