Bond disproportionation and dynamical charge fluctuations in the perovskite rare earth nickelates

摘要

We present a theory describing the local electronic properties of theperovskite rare earth nickelates--materials which have negative charge transferenergies, strong O $2p$ -- Ni $3d$ covalence, and breathing mode latticedistortions at the origin of highly studied metal-insulator andantiferromagnetic ordering transitions. Utilizing a full orbital, fullcorrelation double cluster approach, we find strong charge fluctuations inagreement with a bond disproportionation interpretation. The unique doublecluster formulation permits the inclusion of necessary orbital degeneracies andCoulomb interactions to calculate resonant x-ray spectral responses, with whichwe find excellent agreement with well-established experimental results. Thispreviously absent, crucial link between theory and experiment providesvalidation of the recently proposed bond disproportionation theory, andprovides an analysis methodology for spectroscopic studies of engineered phasesof nickelates and other high valence transition metal compounds.