Orbital Reconstruction and Covalent Bonding at an Oxide Interface

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Abstract
Orbital reconstructions and covalent bonding must be considered as important factors in the rational design of oxide heterostructures with engineered physical properties. We have investigated the interface between high-temperature superconducting (Y,Ca)Ba 2 Cu 3 O 7 and metallic La 0.67 Ca 0.33 MnO 3 by resonant x-ray spectroscopy. A charge of about –0.2 electron is transferred from Mn to Cu ions across the interface and induces a major reconstruction of the orbital occupation and orbital symmetry in the interfacial CuO 2 layers. In particular, the Cu d 3 z 2 – r 2 orbital, which is fully occupied and electronically inactive in the bulk, is partially occupied at the interface. Supported by exact-diagonalization calculations, these data indicate the formation of a strong chemical bond between Cu and Mn atoms across the interface. Orbital reconstructions and associated covalent bonding are thus important factors in determining the physical properties of oxide heterostructures.

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