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

Abstract

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

Antiferromagnetism in Ni‐Based Superconductors

“…[4,37] Following this line of possible connection, the antiferromagnetic exchange interaction may be pivotal for the superconductivity in the NSNO thin films. Although the exact origin of the antiferromagnetism in superconducting NSNO thin films needs more studies, for example, our preliminary calculations that the surface of NSNO films could help stabilize the antiferromagnetic order (see Note S2, Supporting Information), or interface-induced electronic reconstruction [38][39][40][41] could occur at the interface between STO substrates [35,42] and NSNO thin films similar to the LaMnO 3 /STO [43,44] and LaAlO 3 /STO interfaces, [42,45,46] we believe that the experimental observation of the antiferromagnetic order superconducting NSNO thin films itself is fundamentally crucial so that this work may steer the center of focus for the rapidly developing field on the novel superconductivity in nickelates. In addition to the great interest in the community of condensed matter physics, the successful synthesis of this new type of Ni-based superconductors may pave the way to other important novel material applications such as energy, electromagnetic and spintronic materials and devices.…”

Experimental progress on the emergent infinite-layer Ni-based superconductors

“…Oxygen vacancies play important roles in oxides including catalysis [109][110][111][112], gas sensor applications [113], energy storage [114,115], electronic states [116] and in oxide interface systems [117][118][119][120][121] such as LaAlO3/SrTiO3 interfaces [122,123]. In the superconducting Nd0.8Sr0.2NiO2/SrTiO3 superconducting system, oxygen vacancies may be generated during the soft chemical reduction, which could contribute conducting channels and thus affect superconducting transitions.…”

Regulation of hydrogen evolution performance of titanium oxide–carbon composites at high current density with a Ti–O hybrid orbital

“…29 Many studies have shown that metal-oxygen hybridization can tune the catalyst surface chemical environment, affecting the specific transition state on the catalyst surface for the production of the target product. 30,31 However, the HER mechanism of transition-metal oxides, such as metal-oxygen hybrids, and the fundamental parameters that dominate the HER activity still remain unclarified. 32 Meanwhile, to the best of our knowledge, few studies have reported the HER performance of Ti-based materials at high current densities, especially the fundamental parameters that govern the catalytic activity of the electrocatalysts.…”

“…Adjustments of the electronic structures of electrocatalysts are reported to be effective methods for improving HER activity, such as Pr 0.5 (Ba 0.5 Sr 0.5 ) 0.5 Co 0.8 Fe 0.2 O 3‐ δ , 27 SrNb 0.1 Co 0.7 Fe 0.2 O 3‐ δ (nanorods), 28 and cobalt(II) oxide (nanorods) 29 . Many studies have shown that metal–oxygen hybridization can tune the catalyst surface chemical environment, affecting the specific transition state on the catalyst surface for the production of the target product 30,31 . However, the HER mechanism of transition‐metal oxides, such as metal–oxygen hybrids, and the fundamental parameters that dominate the HER activity still remain unclarified 32 .…”