Comparative soft-x-ray resonant-photoemission study on Bi2Sr2CaCu2O8, CuO, and Cu2O

Strong O 1s and Cu 2p resonant enhancements are observed in the valence-band photoemission spectra of ${\mathrm{Bi}}_2$ ${\mathrm{Sr}}_2$ ${\mathrm{CaCu}}_2$ ${\mathrm{O}}_8$, CuO, and ${\mathrm{Cu}}_2$O. The results can be accounted for by a model Hamiltonian with similar parameters but different band filling. The O 1s (Cu 2p) resonant enhancements are found to be dominated by local O 2${\mathit{p}}^4$ (Cu 3${\mathit{d}}^8$) final states reached via local intra-atomic processes; interatomic O-to-Cu resonance processes are found to play only a minor role. It is demonstrated that enhancements observed at 0–1.5 eV binding energies in angle-resolved photoemission of ${\mathrm{Bi}}_2$ ${\mathrm{Sr}}_2$ ${\mathrm{CaCu}}_2$ ${\mathrm{O}}_8$ with the photon energy tuned at 18 eV cannot be attributed to an O 2s resonance effect.