Anomalous enhancement ofBi2Sr2CaCu2O8Fermi-level states near the O 2sthreshold

Photoemission studies of the (001) face of the high-temperature superconductor ${\mathrm{Bi}}_2$ ${\mathrm{Sr}}_2$ ${\mathrm{CaCu}}_2$ ${\mathrm{O}}_8$ 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.