Direct Observation of Charge Order in an EpitaxialNdNiO3Film

Abstract
The first direct observation of charge order of Ni3+δ and Ni3δ by resonant x-ray scattering experiments in an epitaxial film of NdNiO3 is reported. A quantitative value of δ+δ=(0.45±0.04)e was obtained. The temperature dependence of the charge order deviates significantly from those of the magnetic moment and crystallographic structure. This might be an indication of a difference in their fluctuation time scales. These observations are discussed in terms of the temperature-driven metal-insulator transition in the RNiO3 family.