Anomalous enhancement of Bi2Sr2CaCu2O8 Fermi-level states near the O 2s threshold

Photoemission studies of the (001) face of the high-temperature superconductor Bi2Sr2CaCu2O8 have been performed over the photon energy range 16.5--19 eV. Such spectra have previously been analyzed in terms of O 2s resonant photoemission behavior and used to assign O 2p character to features close to the Fermi level. We show that these results may be significantly influenced by the presence of Sr 4p and O 2s core-level peaks created by a small second-order component of the exciting radiation. This could provide an explanation for the anomalous enhancement of states close to the Fermi level recently reported by Wells et al