Electronic Character of Charge Order in Square-Planar Low-Valence Nickelates
Yao Shen, Jennifer Sears, G. Fabbris, Jiemin Li, Jonathan Pelliciari, Matteo Mitrano, Wei He, Junjie Zhang, J. F. Mitchell, Valentina Bisogni, M. R. Norman, Steven Johnston, M. P. M. Dean
Abstract
Charge order is a central feature of the physics of cuprate superconductors and is known to arise from a modulation of holes with primarily oxygen character. Low-valence nickelate superconductors also host charge order, but the electronic character of this symmetry breaking is unsettled. Here, using resonant inelastic x-ray scattering at the Ni L2 edge, we identify intertwined involvements of Ni 3dx2-y2, 3d3z2-r2, and O 2pσ orbitals in the formation of diagonal charge order in an overdoped low-valence nickelate La4Ni3O8. The Ni 3dx2-y2 orbitals, strongly hybridized with planar O 2pσ, largely shape the spatial charge distribution and lead to Ni site-centered charge order. The 3d3z2-r2 orbitals play a small, but non-negligible role in the charge order as they hybridize with the rare-earth 5d orbitals. Our results reveal that the low-energy physics and ground-state character of these nickelates are more complex than those in cuprates.