ANALYSIS OF PHOTOEMISSION DATA FOR CUO - REVISION OF THE CONFIGURATION-ENERGY SCHEME FOR CUPRATE MATERIALS

The valence-band photoemission and BIS data for CuO, from Sawatzky and co-workers, is reanalyzed using a refined version of their impurity-model treatment. The 2p-removal spectrum is carefully calculated, as well as the 3d-removal spectrum. Because a tight-binding treatment of the 2p states provides sharp spectral features, and because much of this 2p spectrum is unaffected by hybridization with the copper 3d′s, this provides a distinct marker which serves to clearly determine the charge-transfer energy parameter Δ. We find that Δ ≳ U, in contrast to previous studies of cuprates and related transition-metal compounds. The final-state configuration energy ordering is therefore E(d8) ≲ E(d9L) ≪ E(d10L2). The well-known claim that the doping-induced holes in cuprate superconductors (La2-xSrx CuO4, for example) are hosted almost entirely within 2p orbitals is thus disproved. The various kinds of opposing evidence are examined, and reasons for discounting their validity are presented. © 1990.