Electronic Character of Charge Order in Square-Planar Low-Valence Nickelates

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 NiL2edge, we identify intertwined involvements of Ni3dx2−y2,3d3z2−r2, and O2pσorbitals in the formation of diagonal charge order in an overdoped low-valence nickelateLa4Ni3O8. The Ni3dx2−y2orbitals, strongly hybridized with planar O2pσ, largely shape the spatial charge distribution and lead to Ni site-centered charge order. The3d3z2−r2orbitals play a small, but non-negligible role in the charge order as they hybridize with the rare-earth5dorbitals. Our results reveal that the low-energy physics and ground-state character of these nickelates are more complex than those in cuprates.