Role of Oxygen States in the Low Valence Nickelate La4Ni3O8
Role of Oxygen States in the Low Valence Nickelate La4Ni3O8
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DOI：
10.1103/physrevx.12.011055
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发表时间：
2022-03-22
影响因子：
12.5
通讯作者：
Dean, M. P. M.
中科院分区：
文献类型：
--
作者：
Shen, Y.;Sears, J.;Dean, M. P. M.
在正方形平面低价镍酸盐中超导电性的发现引发了关于其基本电子性质的激烈辩论：这些材料是否具有类似于铜酸盐的明显的氧电荷转移特性，或者它们是否处于独特的Mott-Hubbard体系中，其中氧起最小的作用？在这里，我们用O K边共振非弹性x射线散射(RIXS)测量了低价镍盐La4Ni3O8和典型的铜酸盐La2-xSrxCuO4(x=0.35)，解决了这个问题。正如预期的那样，铜酸盐位于Zaanen-Sawatzky-Allen(ZSA)方案的电荷转移机制的深处。然而，用ZSA方法的任一种极限都不能很好地描述镍酸盐，发现它具有混合电荷转移-Mott-Hubbard性质，库仑斥力U与电荷转移能A的大小相似。然而，La4Ni3O8的过渡金属-氧跃迁比La2-xSrxCuO4大，导致了显著的超交换作用和明显的配体O轨道的空穴占据，尽管它的Delta较大。我们的结果阐明了低价镍酸盐的本质特征，并对这些材料中超导电性的理论解释提出了强烈的限制。
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 A. 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 Delta. Our results clarify the essential characteristics of low valence nickelates and put strong constraints on theoretical interpretations of superconductivity in these materials.