Nickel-based superconductors provide a long-awaited experimental platform to explore possible cuprate-like superconductivity. Despite similar crystal structure and d electron filling, however, superconductivity in nickelates has thus far only been stabilized in thin-film geometry, raising questions about the polar interface between substrate and thin film. Here we conduct a detailed experimental and theoretical study of the prototypical interface between Nd1−xSrxNiO2 and SrTiO3. Atomic-resolution electron energy loss spectroscopy in the scanning transmission electron microscope reveals the formation of a single intermediate Nd(Ti,Ni)O3 layer. Density functional theory calculations with a Hubbard U term show how the observed structure alleviates the polar discontinuity. We explore the effects of oxygen occupancy, hole doping and cation structure to disentangle the contributions of each for reducing interface charge density. Resolving the non-trivial interface structure will be instructive for future synthesis of nickelate films on other substrates and in vertical heterostructures.
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The experimental data relevant to the findings of this paper have been deposited in the Platform for the Accelerated Realization, Analysis, and Discovery of Interface Materials (PARADIM) database at https://doi.org/10.34863/nf7t-jj61. Additional data, including that contained in Supplementary Information and results of the DFT + U calculations, are available upon reasonable request to the authors.
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B.H.G. and L.F.K. acknowledge support from the Department of Defense Air Force Office of Scientific Research (FA 9550-16-1-0305; L.F.K.) and the Packard Foundation. This work made use of the Cornell Center for Materials Research Shared Facilities, which are supported through the NSF MRSEC Program (DMR-1719875; L.F.K.). The FEI Titan Themis 300 was acquired with support from NSF (NSF-MRI-1429155; L.F.K.), with additional support from Cornell University, the Weill Institute and the Kavli Institute at Cornell. The Thermo Fisher Helios G4 UX focused ion beam was acquired with support from the National Science Foundation Platform for Accelerated Realization, Analysis, and Discovery of Interface Materials (Cooperative Agreement DMR-1539918; L.F.K.). B.G. and R.P. acknowledge support from the German Research Foundation (DFG) within CRC/TRR 80 (107745057; R.P.). Projects G3 and G8 and computational time at magnitUDE were granted by the Center for Computational Sciences and Simulation of the University of Duisburg-Essen (DFG Grant INST 20876/209-1 FUGG; R.P.). The work at SLAC/Stanford is supported by the US Department of Energy, Office of Basic Energy Sciences, Division of Materials Sciences and Engineering (DE-AC02-76SF00515; H.Y.H.) and the Gordon and Betty Moore Foundation’s Emergent Phenomena in Quantum Systems Initiative (GBMF9072 for synthesis equipment; H.Y.H.). M.O. acknowledges partial financial support from the Takenaka Scholarship Foundation.
The authors declare no competing interests.
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Goodge, B.H., Geisler, B., Lee, K. et al. Resolving the polar interface of infinite-layer nickelate thin films. Nat. Mater. 22, 466–473 (2023). https://doi.org/10.1038/s41563-023-01510-7