The discovery of superconductivity in square-planar low valence nickelates has ignited a vigorous debate regarding their essential electronic properties: Do these materials have appreciable oxygen charge-transfer character akin to the cuprates, or are they in a distinct Mott-Hubbard regime where oxygen plays a minimal role? Here, we resolve this question using O K-edge resonant inelastic X-ray scattering (RIXS) measurements of the low valence nickelate La4Ni3O8 and a prototypical cuprate La2-xSrxCuO4 (x=0.35). As expected, the cuprate lies deep in the charge-transfer regime of the Zaanen-Sawatzky-Allen (ZSA) scheme. The nickelate, however, is not well described by either limit of the ZSA scheme and is found to be of mixed charge-transfer-Mott-Hubbard character with the Coulomb repulsion U of similar size to the charge-transfer energy Δ. Nevertheless, the transition-metal-oxygen hopping is larger in La4Ni3O8 than in La2-xSrxCuO4, leading to a significant superexchange interaction and an appreciable hole occupation of the ligand O orbitals in La4Ni3O8 despite its larger Δ. Our results clarify the essential characteristics of low valence nickelates and put strong constraints on theoretical interpretations of superconductivity in these materials.
Role of Oxygen States in the Low Valence Nickelate La4Ni3O8 / Shen, Y., Sears, J., Fabbris, G., Li, J., Pelliciari, J., Jarrige, I., He, X.i., Božović, I., Mitrano, M., Zhang, J., Mitchell, J. f., Botana, A. s., Bisogni, V., Norman, M. r., Johnston, S., Dean, M. p. m.. - In: PHYSICAL REVIEW. X. - ISSN 2160-3308. - 12:1(2022), pp. 1-13. [10.1103/physrevx.12.011055]
Role of Oxygen States in the Low Valence Nickelate La4Ni3O8
Shen, Y.;Li, J.;Pelliciari, J.;
2022
Abstract
The discovery of superconductivity in square-planar low valence nickelates has ignited a vigorous debate regarding their essential electronic properties: Do these materials have appreciable oxygen charge-transfer character akin to the cuprates, or are they in a distinct Mott-Hubbard regime where oxygen plays a minimal role? Here, we resolve this question using O K-edge resonant inelastic X-ray scattering (RIXS) measurements of the low valence nickelate La4Ni3O8 and a prototypical cuprate La2-xSrxCuO4 (x=0.35). As expected, the cuprate lies deep in the charge-transfer regime of the Zaanen-Sawatzky-Allen (ZSA) scheme. The nickelate, however, is not well described by either limit of the ZSA scheme and is found to be of mixed charge-transfer-Mott-Hubbard character with the Coulomb repulsion U of similar size to the charge-transfer energy Δ. Nevertheless, the transition-metal-oxygen hopping is larger in La4Ni3O8 than in La2-xSrxCuO4, leading to a significant superexchange interaction and an appreciable hole occupation of the ligand O orbitals in La4Ni3O8 despite its larger Δ. Our results clarify the essential characteristics of low valence nickelates and put strong constraints on theoretical interpretations of superconductivity in these materials.
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