Depth-Resolved Modulation of Metal-Oxygen Hybridization and Orbital Polarization across Correlated Oxide Interfaces

Interface-induced modifications of the electronic, magnetic, and lattice degrees of freedom drive an array of novel physical properties in oxide heterostructures. Here, large changes in metal-oxygen band hybridization, as measured in the oxygen ligand hole density, are induced as a result of interfacing two isovalent correlated oxides. Using resonant X-ray reflectivity, a superlattice of SrFeO₃ and CaFeO₃ is shown to exhibit an electronic character that spatially evolves from strongly O-like in SrFeO₃ to strongly Fe-like in CaFeO₃ . This alternating degree of Fe electronic character is correlated with a modulation of an Fe 3d orbital polarization, giving rise to an orbital superstructure. At the SrFeO₃ /CaFeO₃ interfaces, the ligand hole density and orbital polarization reconstruct in a single unit cell of CaFeO₃ , demonstrating how the mismatch in these electronic parameters is accommodated at the interface. These results provide new insight into how the orbital character of electrons is altered by correlated oxide interfaces and lays out a broadly applicable approach for depth-resolving band hybridization.