Observation of strong electron correlations in YBa2Cu3O7-δ by hν dependent photoelectron spectroscopy

After a review of the understanding of resonant photoemission phenomena we present photoemission spectra from single phase YBa2Cu3O7-δ which have been measured in the photon energy range 17-130 eV, at T=80 K, T=300 K and intermediate temperatures using synchrotron radiation. Intense satellites associated with the Cu 3d and O 2p bands are observed to undergo resonance at the Cu 3p and O 2s core level excitation thresholds respectively indicating the presence of holes in the Cu and O hybrid bands of both Cu and O sites. The strong correlation effects for the valence electron suggest that one electron calculations may not be appropriate for a detailed description of the electronic properties of this material. (author). 23 refs, 9 figs, 1 tab