Role of Oxygen States in the Low Valence Nickelate La\(_4\)Ni\(_3\)O\(_8\)

• Published in: arXiv.org 2022-02
• Main Authors: Shen, Y, Sears, J, Fabbris, G, J Li, Pelliciari, J, Jarrige, I, He, Xi, Bozovic, I, Mitrano, M, Zhang, Junjie, Mitchell, J F, Botana, A S, Bisogni, V, Norman, M R, Johnston, S, Dean, M P M
• Format: Article
• Language: English
• Subjects: Charge transfer; Cuprates; Nickel; Oxygen; Strontium; Superconductivity; Transition metals
• ISSN: 2331-8422
• DOI: 10.48550/arxiv.2110.08937

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 La\(_{4}\)Ni\(_{3}\)O\(_{8}\) and a prototypical cuprate La\(_{2-x}\)Sr\(_{x}\)CuO\(_{4}\) (\(x=0.35\)). As expected, the cuprate lies deep in the charge-transfer regime of the Zaanen-Sawatzky-Allen 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 \(\Delta\). Nevertheless, the transition-metal-oxygen hopping is larger in La\(_{4}\)Ni\(_{3}\)O\(_{8}\) than in La\(_{2-x}\)Sr\(_{x}\)CuO\(_{4}\), leading to a significant superexchange interaction and an appreciable hole occupation of the ligand O orbitals in La\(_{4}\)Ni\(_{3}\)O\(_{8}\) despite its larger \(\Delta\). Our results clarify the essential characteristics of low valence nickelates and put strong constraints on theoretical interpretations of superconductivity in these materials.