Electronic Structure of a Delafossite Oxide CuAlO${}_2$ in Comparison with CuCrO${}_2$

Abstract

We investigated the electronic structure of a delafossite oxide CuAlO${}_2$ in comparison with CuCrO${}_2$, using vacuum ultraviolet (VUV) and hard x-ray (HX) photoemission spectroscopy (PES) and band structure calculations within the local-density approximation +$U$ scheme. Cu 3$p-3d$ resonant PES and Cu $2p$ core-level HX-PES give concrete evidence that the Cu valence in CuAlO${}_2$ is monovalent, which makes a sharp contrast to CuCrO${}_2$ that showed contradictory results depending upon probing methods [Yokobori \textit{et al.}, Phys. Rev. B \textbf{87}, 195124 (2013)]. We further noticed weak but detectable satellite structures due to Cu${}^{2+}$ state in the Cu $2p$ HX-PES spectrum of CuCrO${}_2$, surprisingly, without an observable main peak due to the Cu${}^{2+}$ state. Comparisons between the valence-band HX-PES spectra and the band structure calculations revealed a significant amount of the Cu $4s$ and Al $3s$/Cr $4s$ states in the valence band. The above results can reasonably be explained by the Cu $3d,4s-$Cr $3d$ charge transfer model that we previously proposed in the above paper, thereby demonstrating the critical role of empty $3d$ orbitals in the electronic structure of the copper delafossite oxides.

7 pages, 6 figures

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Cited by in corpus (1)

• Realistic Simulation of Valence-band Photoemission Spectra by using First-principles Calculations on the Basis of FLAPW Method