Theory of Electron Correlation in 3d Transition Metal Oxides

3d還移金属酸化物における電子相関の理論

田中 新

Electronic structures and spectral functions of 3d transition metal (TM) oxides are theoretically investigated using a finite size cluster model. We first study the resonant 3d, 3p and 3s photoemisson spectroscopies (PES) at TM 2p threshold in late 3d TM monoxides and TiO2 using a cluster model with a TM ion and its ligand oxygen ions which includes the configuration interaction and the 3d-3d and 3d-core hole multipole interaction. Analyzing the experimental valence band spectra, we determine the charge transfer energy and the 3d-3d Coulomb interaction energy and show that the spectra give reliable information about the characteristic parameters of TM oxides. We also discuss the difference in the selection rule between the direct process and the resonance process.

We next discuss the 3d PES, 3d inverse photoemission spectroscopy (IPES) and Cu 2p X-ray photoemission spectroscopy (XPS) spectra for the CuO2 plane in the undoped and doped high-Tc superconductors using a CunOm cluster model containing up to four Cu ions. The model takes into account full degeneracy of the Cu 3d and O 2p orbits and on-site Cu 3d-3d and O 2p-2p electrostatic multipole interaction. For the 3d PES spectra of the undoped cluster, the main peak structure consists of two kinds of states. One has an excess hole introduced by the photoexcitation on nearest neighbor oxygen sites of the photoexcited Cu site. The other has the hole on neighboring CuO4 units, having the Zhang-Rice singlet state on the neighboring units. Because of the non-local character of the state corresponding to the main peak structure, the structure is sensitive to the number of the nearest neighbor Cu site. The interference of the initial and final state wave functions caused by the inter-CuO4-unit charge transfer lead to a spectral weight transfer to the low binding energy side. For the Cu 2p XPS spectra for undoped systems, a hole escaping from the core hole Cu site exhibits similar way and its main peak structure consists of the two kinds of screened states. In the light of calculations for larger clusters, the results obtained from the above small clusters are reinterpreted. For the 3d PES spectra of the electron doped cluster, two kinds of states are created inside the insulating gap and the chemical potential moves into the conduction band. The spectral weight is transferred to the peaks corresponding to the states created inside insulating gap, drastically.

We furthermore present a formalism for a systematic basis set reduction of clusters. Using this formalism, we calculate the spectra of the clusters containing up to five Cu ions, where the number of basis set without the reduction beyond the tractable limit. We show that our formalism is a promising method to discuss spectral functions in large clusters including 3d TM ions other than Cu ion.

電気工学 [ 540 ]

英語

Copyright(c) by Author

(1) Resonant 3d, 3P and 3s Photoemission in Transition Metal Oxides Predicted at 2p Threshold (遷移金属酸化物の2pしきい値領域における共鳴3d,3pおよび3s光電子放出の予言), 共著者 田中新、城健男, (学会誌) Journal of the Physical Society of Japan Vol.63, No.7, pp.2788-2807 平成6年7月15日出版 (日本物理学会) ～を参照している

(2) Strong 3d-Ligand Hybridization in TiO2 and Satellite Structures in Ti 3d and 3p Photoemission (Tio2における3d-配位子間の強い混成とTi3dおよび3p光電子分光放出のサテライト構造), 共著者 城健男、田中新, (学会誌) Journal of the Physical Society of Japan Vol.64, No.2, pp.676-677 平成7年2月15日出版 (日本物理学会) ～を参照している

(3) Efrect of Electron Doping on Spectral Function of Cu-Oxide Cluster Model Including Full Multiplet: Shift of Valence Band Edge (銅酸化物クラスター模型におけるスペクトル関数の電子ドープ効果～価電子帯上端の移動～), 共著者 田中新、城健男, (学会誌) Journal of the Physical Society of Japan Vol.65, No.4, pp.912-915 平成8年4月15日出版 (日本物理学会) ～を参照している

(4) Spectral Function of Electron-Doped Cu-Oxide Cluster Model Including Full Multiplet (多重極相互作用を取り入れ、電子をドープした銅酸化物クラスター模型におけるスペクトル関数), 共著者 田中新、城健男, (学会誌) Physica Bに平成9年出版予定 (Elsevier Science) ～を参照している

[DOI] http://dx.doi.org/10.1143/JPSJ.63.2788 ～を参照している

[DOI] http://dx.doi.org/10.1143/JPSJ.64.676 ～を参照している

[DOI] http://dx.doi.org/10.1143/JPSJ.65.912 ～を参照している

[DOI] http://dx.doi.org/10.1016/S0921-4526(97)00240-8 ～を参照している

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