Superconductivity in a quintuple-layer square-planar nickelate

Since the discovery of high-temperature superconductivity in the copper oxide materials, there have been sustained efforts to both understand the origins of this phase and discover new cuprate-like superconductors.  One prime materials candidate has been the rare-earth nickelates and indeed superconductivity was recently discovered in the doped compound Nd_0.8Sr_0.2NiO₂.  Undoped NdNiO₂ belongs to a series of layered square-planar nickelates with chemical formula Nd_n+1Ni_nO_2n+2 and is known as the ‘infinite-layer’ (n = ∞) nickelate. Here, using reactive oxide molecular beam epitaxy, which provides atomic level layer-by-layer control of thin film synthesis, we design and synthesize the quintuple-layer (n = 5) member of this series, Nd₆Ni₅O₁₂, which achieves optimal cuprate-like electron filling (3d^8.8) without chemical doping.  We observe a superconducting transition beginning at ~13 K.  Electronic structure calculations, in tandem with magnetoresistive and spectroscopic measurements, suggest that Nd₆Ni₅O₁₂ interpolates between cuprate-like and infinite-layer nickelate-like behavior.  In engineering a distinct superconducting nickelate, we identify the square-planar nickelates as a new family of superconductors which can be tuned via both doping and dimensionality.