Electronic structure of (LaNiO3)2/(LaAlO3)Nheterostructures grown along [111

Abstract

The electronic structure of a LaNiO${}_{3}$ bilayer grown along the [111] direction and confined between insulating layers of LaAlO${}_{3}$ is theoretically investigated using a combination of first-principles calculations and effective multiorbital lattice models. The local density approximation (LDA) band structure is well reproduced by a tight-binding model for the Ni ${e}_{g}$ orbitals defined on the buckled honeycomb lattice. We highlight peculiar properties of this model, which include almost flat bands as well as linear and quadratic band-crossing points. The effect of local correlations is discussed within the LDA$+U$ scheme and within the Hartree-Fock approximation for interacting multiorbital lattice models. Over a wide range of interaction parameters, we find that a ferromagnetic phase is energetically favored. We discuss the possibility of additional orbital order, which could stabilize a spontaneous Chern insulator with chiral edge modes or a staggered orbital phase with a $\sqrt{3}\ifmmode\times\else\texttimes\fi{}\sqrt{3}$ reconstruction of the unit cell. By studying an interacting nickel-oxygen lattice model, we find that the stability of these orbitally ordered phases also depends on the value of the charge-transfer energy. Controlling the charge-transfer energy might therefore be an important step towards engineering exotic electronic phases in certain classes of oxide heterostructures.