Strong Orbital Polarization in a Cobaltate-Titanate Oxide Heterostructure

Through a combination of experimental measurements and theoretical modeling, we describe a strongly orbital-polarized insulating ground state in an ${({\mathrm{LaTiO}}_{3})}_{2}/{({\mathrm{LaCoO}}_{3})}_{2}$ oxide heterostructure. X-ray absorption spectra and ab initio calculations show that an electron is transferred from the titanate to the cobaltate layers. The charge transfer, accompanied by a large octahedral distortion, induces a substantial orbital polarization in the cobaltate layer of a size unattainable via epitaxial strain alone. The asymmetry between in-plane and out-of-plane orbital occupancies in the high-spin cobaltate layer is predicted by theory and observed through x-ray linear dichroism experiments. Manipulating orbital configurations using interfacial coupling within heterostructures promises exciting ground-state engineering for realizing new emergent electronic phases in metal oxide superlattices.