Electronic structure of hole-doped delafossite oxides CuCr_{1-x}Mg_{x}O_{2}

TL;DR

This study investigates the electronic structure of hole-doped CuCr_{1-x}Mg_{x}O_{2} delafossite oxides using spectroscopy and calculations, revealing the dominant Cr 3d character of doped holes and complex charge transfer involving Cu states.

Contribution

It provides a detailed analysis of the electronic structure and charge transfer mechanisms in hole-doped delafossite oxides, highlighting the role of Cr 3d and Cu 3d, 4s states.

Findings

Doped holes mainly have Cr 3d character.

Cu valence remains monovalent at low doping levels.

Complex charge transfer involves Cu 4s and 3d states.

Abstract

We report the detailed electronic structure of a hole-doped delafossite oxide CuCr_{1-x}Mg_{x}O_{2} (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 Cr^{3+} 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^{+} (3d^{10}) and Cu^{2+} (3d^{9}) like initial states in Cu 2p-3d resonant PES spectrum for 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 no 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.