Metal-to-non-metal transitions in high-temperature oxide superconductors monitored by photoelectron spectroscopy

Metal-to-non-metal transitions induced in Bi-Sr-Ca-Cu-O by cation substitution and in Y-Ba-Cu-O by oxygen deficiency are used to show that changes in the Cu 2p signature in X-ray photoemission may be correlated with the changes in the hole doping level on the Cu-O2 planes of these high-temperature superconducting oxides. Parallel core and valence studies of the transition in the Bi-Sr-Ca-Cu-O material suggest that some of the introduced holes may be present on the Bi-O planes in the superconducting state.