Jahn-Teller physics and orbital control in oxide heterostructures: a first-principles study of LaNiO$_3$/LaXO$_3$ (X= B, Al, Ga, In)

Generalized Gradient Approximation (GGA) density functional calculations are used to show that different choices of spacer layer $LaXO_3$ in LaNiO$_3$/LaXO$_3$ heterostructures lead to different relative occupancies of Ni $3z^2-r^2$ and $x^2-y^2$ orbitals, with the sign of the orbital polarization even reversing as the B-site atom in the spacer layer is changed from $X=B$ through $Al,Ga$ to $In$. The crucial role played by the hybridization of the apical oxygen to the spacer layer (LaXO$_3$) is demonstrated. Extensions to other systems and implications for many-body calculations are discussed.