J. Phys. Soc. Jpn. 88, 074701 (2019) [6 Pages]
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Electronic Structure of a Delafossite Oxide CuAlO2 in Comparison with CuCrO2

Kenta Takahashi1, Ryo Kato1, Mario Okawa1,, Tetsuji Okuda2, Akira Yasui3, Eiji Ikenaga4, Kanta Ono5, Noriaki Hamada6,7, and Tomohiko Saitoh1,
+ Affiliations
1Department of Applied Physics, Tokyo University of Science, Katsushika, Tokyo 125-8585, Japan2Department of Electrical and Electronics Engineering, Kagoshima University, Kagoshima 890-0065, Japan3Japan Synchrotron Radiation Research Institute, Sayo, Hyogo 679-5198, Japan4Institute of Materials and Systems for Sustainability, Nagoya University, Nagoya 464-8601, Japan5Photon Factory, KEK, Tsukuba, Ibaraki 305-0801, Japan6Department of Physics, Tokyo University of Science, Noda, Chiba 278-8510, Japan7Center for Spintronics Research Network, Osaka University, Toyonaka, Osaka 560-8531, Japan
Received September 3, 2018; Accepted May 7, 2019; Published June 14, 2019

We investigated the electronic structure of a delafossite oxide CuAlO2 in comparison with CuCrO2, using vacuum ultraviolet (VUV) and hard x-ray (HX) photoemission spectroscopy (PES) and band structure calculations within the local-density approximation +U scheme. Cu 3p–3d resonant PES and Cu 2p core-level HX-PES give concrete evidence that the Cu valence in CuAlO2 is monovalent, which makes a sharp contrast to CuCrO2 that showed contradictory results depending upon probing methods [Yokobori et al., Phys. Rev. B 87, 195124 (2013)]. We further noticed weak but detectable satellite structures due to Cu2+ state in the Cu 2p HX-PES spectrum of CuCrO2, surprisingly, without an observable main peak due to the Cu2+ 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.

©2019 The Physical Society of Japan
https://doi.org/10.7566/JPSJ.88.074701

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