Orbital order and possible superconductivity in LaNiO3/LaMO3 superlattices

A hypothetical layered oxide La_2NiMO_6 where NiO_2 and MO_2 planes alternate along the c-axis of ABO_3 perovskite lattice is considered theoretically. Here, M denotes a trivalent cation Al, Ga,... such that MO_2 planes are insulating and suppress the c-axis charge transfer. We predict that correlated e_g electrons in the NiO_2 planes develop a planar x^2-y^2 orbital order driven by the reduced dimensionality and further supported by epitaxial strain from the substrate. Low energy electronic states can be mapped to a single-band t-t'-J model, suggesting favorable conditions for high-T_c superconductivity.