Absence of 3a charge density wave order in the infinite-layer nickelate NdNiO.

A hallmark of many unconventional superconductors is the presence of many-body interactions that give rise to broken-symmetry states intertwined with superconductivity. Recent resonant soft X-ray scattering experiments report commensurate 3a charge density wave order in infinite-layer nickelates, which has important implications regarding the universal interplay between charge order and superconductivity in both cuprates and nickelates. Here we present X-ray scattering and spectroscopy measurements on a series of NdNiO samples, which reveal that the signatures of charge density wave order are absent in fully reduced, single-phase NdNiO. The 3a superlattice peak instead originates from a partially reduced impurity phase where excess apical oxygens form ordered rows with three-unit-cell periodicity. The absence of any observable charge density wave order in NdNiO highlights a crucial difference between the phase diagrams of cuprate and nickelate superconductors.