Two Distinct Charge Orders in Infinite-Layer PrNiO_2+δ Revealed by Resonant X-Ray Diffraction

Abstract Research of infinite-layer nickelates has unveiled a broken translation symmetry, which has sparked significant interest in its root, its relationship to superconductivity, and its comparison to charge order in cuprates. In this study, resonant x-ray scattering measurements were performed on thin films of infinite-layer PrNiO_2+δ. The results show significant differences in the superlattice reflection at the Ni L₃ absorption edge compared to that at the Pr M₅ resonance in their dependence on energy, temperature, and local symmetry. These differences point to two distinct charge orders, although they share the same in-plane wavevectors. It is suggested that these dissimilarities could be linked to the excess oxygen dopants, given that the resonant reflections were observed in an incompletely reduced PrNiO_2+δ film. Furthermore, azimuthal analysis indicates that the oxygen ligands likely play a crucial role in the charge modulation revealed at the Ni L₃ resonance.