orbital degrees of freedom and produce emergent electronic and magnetic properties in TMOs, [1][2][3][4] a key question is what role do the underlying changes in metaloxygen hybridization play? This uncertainty remains because while electronic and magnetic properties can be measured by existing techniques, metal-oxygen hybridization cannot be thus far probed in a quantitative manner across interfaces. Here, we deploy resonant soft X-ray reflectivity to depth resolve the oxygen ligand hole density arising from metal-oxygen hybridization and reveal that a superlattice consisting of two TMOs with similar electronic structures unexpectedly exhibits large changes in orbital character. By resolving the orbital character at the unit cell level, we find that the disparate orbital characters reconstruct at the interface, thus demonstrating a new class of oxide interfacial reconstructions, that of metal-oxygen hybridization.The important role of metal-oxygen hybridization is highlighted by the anomalous behavior of TMOs with strong metal-oxygen covalency. These materials have metal d and O p bands that directly overlap in energy-leading to a small or negative charge transfer energy-and gives rise to self-doped oxygen ligand holes due to the energetically favorable transfer 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 SrFeO 3 and CaFeO 3 is shown to exhibit an electronic character that spatially evolves from strongly O-like in SrFeO 3 to strongly Fe-like in CaFeO 3 . 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 SrFeO 3 /CaFeO 3 interfaces, the ligand hole density and orbital polarization reconstruct in a single unit cell of CaFeO 3 , 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.
Band HybridizationThe hybridization between transition metal d states and O p states is one of the defining features of transition metal oxides (TMOs) compared to conventional band insulators and metals, and the resulting mixed metal/oxygen character of the electronic structure plays a key role in their electronic properties. While it has been thoroughly demonstrated that formation of heterostructures can alter the charge, spin, and