Depth-profiling metal-oxygen hybridization and orbital polarization in isovalent perovskite oxide heterostructures

Heterostructures of complex oxides have been successfully deployed to realize new electronic properties, with much of this work motivated by interfacial charge transfer effects that change the local charge density. Here, we synthesized superlattices of the isovalent perovskite oxides SrFeO₃ and CaFeO₃ using molecular beam epitaxy to investigate structural-induced changes in the orbital character of carriers across oxide interfaces while retaining the same nominal charge density. Using resonant x-ray reflectivity at the oxygen K-edge, we demonstrate that the Fe-O hybridization in CaFeO₃ and SrFeO₃ differs and is additionally modified at the interface. Further, using linearly polarized photons we find that the reflectivity at the Fe L-edge is polarization-dependent, which is attributed to strain-induced orbital polarization in the Fe 3d electron orbitals. By modeling the resonant reflectivity, we correlate changes in the Fe orbital polarization with changes in the Fe-O hybridization across the SrFeO₃-CaFeO₃ interface and reveal the presence of a hybridization superstructure.