Superconducting Phase Diagram of Multi-Layer Square-Planar Nickelates

The discovery of superconductivity in square-planar nickelates has offered a rich materials platform to explore the origins of cuprate-like superconductivity. Experimental investigations however have largely been limited to within the infinite-layer <i>R</i>NiO₂ nickelates. Here, we construct a phase diagram of the multi-layer square-planar Nd<i>_n</i>₊₁Ni<i>_n</i>O_2<i>n</i>+2 compounds and discover signatures of a superconducting dome for <i>n</i> = 4 – 8. Upon decreasing the dimensionality <i>n</i>, the superconducting anisotropy evolves due to 4<i>f</i> electron effects, and electronic structure characteristics approach cuprate-like behavior. Magnetic fluctuations persist from within the superconducting dome and into the over-doped, non-superconducting compound. Our work establishes this layered structural template, complementary to chemical doping, for creating new nickel-based superconductors. We indicate underlying commonalities and distinct differences across varying structural realizations of square-planar nickelates.<br/><br/>This work was supported primarily by the US Department of Energy, Office of Basic Energy Sciences, Division of Materials Sciences and Engineering, under Award No. DE-SC0021925. S.F.R.T., M.P.M.D., and M.M. were supported by the US DOE under Award No. DE-SC0012704.