Engineering the Interface of Nickelate Thin Films via MBE and Soft-Chemical Synthesis

Recent observations of rare-earth nickelate superconductivity have established the Ruddlesden-Popper (RP) R_n+1Ni_nO_(3n+1) and reduced square-planar R_n+1Ni_nO_(2n+2) series as important comparisons to the high-T_c cuprates. To date, ambient pressure superconductivity has only been realized in epitaxial nickelate thin films, prompting ongoing inquiry into the role of epitaxy-imparted strain, dimensionality, and interfacial physics in nickelate electronic properties. Here, we synthesize a variety of RP nickelates via reactive oxide molecular beam epitaxy (MBE) with chemical doping and tunable strain states. We also demonstrate new soft-chemical reduction methods to modify the anion sublattice. Through transport measurements and electron microscopy, we investigate emergent electronic phases and corresponding local microstructures particularly at the nickelate and SrTiO₃ substrate interface, and discuss potential implications towards engineering superconductivity in higher-dimensional RP and square-planar systems.<br/>This project was primarily supported by the US Department of Energy, Office of Basic Energy Sciences, Division of Materials Sciences and Engineering, under Award No. DE-SC0021925.