title: Orbital Engineering in Nickelate Heterostructures Driven by Anisotropic Oxygen Hybridization rather than Orbital Energy Levels.
abstract: Resonant inelastic x-ray scattering is used to investigate the electronic origin of orbital polarization in nickelate heterostructures taking LaTiO_{3}-LaNiO_{3}-3×(LaAlO_{3}), a system with exceptionally large polarization, as a model system. We find that heterostructuring generates only minor changes in the Ni 3d orbital energy levels, contradicting the often-invoked picture in which changes in orbital energy levels generate orbital polarization. Instead, O K-edge x-ray absorption spectroscopy demonstrates that orbital polarization is caused by an anisotropic reconstruction of the oxygen ligand hole states. This provides an explanation for the limited success of theoretical predictions based on tuning orbital energy levels and implies that future theories should focus on anisotropic hybridization as the most effective means to drive large changes in electronic structure and realize novel emergent phenomena.
authors.affiliation: Department of Condensed Matter Physics and Materials Science, Brookhaven National Laboratory, Upton, New York 11973, USA.
authors.forename: G
authors.initials: G
authors.lastname: Fabbris
authors.affiliation: Department of Condensed Matter Physics and Materials Science, Brookhaven National Laboratory, Upton, New York 11973, USA.
authors.forename: D
authors.initials: D
authors.lastname: Meyers
authors.affiliation: National Synchrotron Radiation Research Center, Hsinchu 30076, Taiwan.
authors.forename: J
authors.initials: J
authors.lastname: Okamoto
authors.affiliation: Research Department "Synchrotron Radiation and Nanotechnology", Paul Scherrer Institut, CH-5232 Villigen PSI, Switzerland.
authors.forename: J
authors.initials: J
authors.lastname: Pelliciari
authors.affiliation: Department of Applied Physics, Yale University, New Haven, Connecticut 06520, USA.
authors.forename: A S
authors.initials: AS
authors.lastname: Disa
authors.affiliation: Research Department "Synchrotron Radiation and Nanotechnology", Paul Scherrer Institut, CH-5232 Villigen PSI, Switzerland.
authors.forename: Y
authors.initials: Y
authors.lastname: Huang
authors.affiliation: National Synchrotron Radiation Research Center, Hsinchu 30076, Taiwan.
authors.forename: Z-Y
authors.initials: ZY
authors.lastname: Chen
authors.affiliation: National Synchrotron Radiation Research Center, Hsinchu 30076, Taiwan.
authors.forename: W B
authors.initials: WB
authors.lastname: Wu
authors.affiliation: National Synchrotron Radiation Research Center, Hsinchu 30076, Taiwan.
authors.forename: C T
authors.initials: CT
authors.lastname: Chen
authors.affiliation: Department of Applied Physics, Yale University, New Haven, Connecticut 06520, USA.|Department of Mechanical Engineering and Materials Science, Yale University, New Haven, Connecticut 06520, USA.
authors.forename: S
authors.initials: S
authors.lastname: Ismail-Beigi
authors.affiliation: Department of Applied Physics, Yale University, New Haven, Connecticut 06520, USA.|Department of Mechanical Engineering and Materials Science, Yale University, New Haven, Connecticut 06520, USA.
authors.forename: C H
authors.initials: CH
authors.lastname: Ahn
authors.affiliation: Department of Applied Physics, Yale University, New Haven, Connecticut 06520, USA.
authors.forename: F J
authors.initials: FJ
authors.lastname: Walker
authors.affiliation: National Synchrotron Radiation Research Center, Hsinchu 30076, Taiwan.|Department of Physics, National Tsing Hua University, Hsinchu 30013, Taiwan.
authors.forename: D J
authors.initials: DJ
authors.lastname: Huang
authors.affiliation: Research Department "Synchrotron Radiation and Nanotechnology", Paul Scherrer Institut, CH-5232 Villigen PSI, Switzerland.
authors.forename: T
authors.initials: T
authors.lastname: Schmitt
authors.affiliation: Department of Condensed Matter Physics and Materials Science, Brookhaven National Laboratory, Upton, New York 11973, USA.
authors.forename: M P M
authors.initials: MP
authors.lastname: Dean