Orbital Ordering and Correlation Effects in a NdNiO₃/NdAlO₃ Superlattice

Nickel oxide heterostructures in the RNiO₃ family show a complex interplay of structure and electronic correlations that depends on the rare earth atom R, strain and number of layers of the perovskite nickelate. These lead to a metal-insulator transition, magnetic and charge order as well as structural breathing distortions. Recently there has been an effort to engineer the orbital order of nickelates through heterostructuring in such a way as to reproduce the High Tc Cuprate band structure. Experiments on (NdNiO₃)_n/(NdAlO₃)_m superlattices [1] have shown that the magnetic order characteristic of the insulating phase for NdNiO₃ appears for a number of nickelate layers n>1; at n=1 it can no longer be detected. X-Ray measurements have measured orbital polarization in the eg d-shell for n>1 despite a lack of bond symmetry breaking, which we showed can be understood as an effect of anisotropic ionicity [1]. Here we explain the competing roles of quantum confinement, electron correlations and heterostructuring on the NdNiO₃ monolayer through DFT, slave-boson and DMFT methods and model calculations.
[1] Physical Review Materials 1, 024410, 2017