Electronic structure of the hole-doped delafossite oxides CuCr _1-xMg_xO₂

We report the detailed electronic structure of a hole-doped delafossite oxide CuCr_1-xMg_xO₂ (0≤x≤0.03) studied by photoemission spectroscopy (PES), soft x-ray absorption spectroscopy (XAS), and band-structure calculations within the local-density approximation +U (LDA+U) scheme. Cr/Cu 3p-3d resonant PES reveals that the near-Fermi-level leading structure has primarily the Cr 3d character with a minor contribution from the Cu 3d through Cu 3d-O 2p-Cr 3d hybridization, having good agreement with the band-structure calculations. This indicates that a doped hole will have primarily the Cr 3d character. Cr 2p PES and L-edge XAS spectra exhibit typical Cr3⁺ features for all x, while the Cu L-edge XAS spectra exhibited a systematic change with x. This indicates now that the Cu valence is monovalent at x=0 and the doped hole should have Cu 3d character. Nevertheless, we surprisingly observed two types of charge-transfer satellites that should be attributed to Cu⁺ (3d10) and Cu2⁺ (3d9) like initial states in Cu 2p-3d resonant PES spectrum of at x=0, while Cu 2p PES spectra with no doubt shows the Cu⁺ character even for the lightly doped samples. We propose that these contradictory results can be understood by introducing not only the Cu 4s state, but also finite Cu 3d,4s-Cr 3d charge transfer via O 2p states in the ground-state electronic configuration.