Photoemission studies of high-temperature superconductors ${\mathrm{YBa}}_2$${\mathrm{Cu}}_3$${\mathrm{O}}_{7\mathrm{-}\mathrm{\delta }}$, ${\mathrm{GdBa}}_2$${\mathrm{Cu}}_3$${\mathrm{O}}_{7\mathrm{-}\mathrm{\delta }}$, and ${\mathrm{EuBa}}_2$${\mathrm{Cu}}_3$${\mathrm{O}}_{7\mathrm{-}\mathrm{\delta }}$

The electronic structures of three high-temperature superconducting materials, ${\mathrm{YBa}}_2$ ${\mathrm{Cu}}_3$ ${\mathrm{O}}_{7\mathrm{-}\mathrm{\delta }}$, ${\mathrm{GdBa}}_2$ ${\mathrm{Cu}}_3$ ${\mathrm{O}}_{7\mathrm{-}\mathrm{\delta }}$, and ${\mathrm{EuBa}}_2$ ${\mathrm{Cu}}_3$ ${\mathrm{O}}_{7\mathrm{-}\mathrm{\delta }}$, were studied with angle-integrated photoemission. The effects of sample treatment and preparation, including mechanical scraping, ion sputtering, and temperature cycling, were examined. High-resolution spectra were obtained from samples prepared by mechanical scraping at 90 K in the vacuum chamber to minimize contamination and the loss of oxygen. The resonance behavior of the various valence and core states in the photoemission spectra was investigated to identify the atomic origin of the states. The Cu- and O-derived states dominated the valence-band region at low photon energies, as shown by a comparison of the energy distribution curves for all three compounds. The measured density of states at the Fermi edge was very low. All of the spectral features, including the valence bands, core levels, Fermi-edge emission, and the Cu 3d satellites did not show any noticeable changes as a function of sample temperature between 20 and 300 K.