Superconductivity in PrNiO₂ Infinite-Layer Nickelates

Several reports about infinite-layer nickelate thin films suggest that the superconducting critical temperature versus chemical doping phase diagram has a dome-like shape, similar to cuprates. Here, a highly reproducible superconducting state in undoped PrNiO₂ thin films grown on SrTiO₃ are demonstrated. Scanning transmission electron microscopy measurements show coherent infinite-layer phase with no visible stacking-fault defects, an overall high structural quality where possible unintentional chemical doping or interstitial oxygen, if present, sum well below the measurable threshold of the technique. X-ray absorption measurements show very sharp features at the Ni L_3,2-edges with a large linear dichroism, indicating the preferential hole occupation of Ni¹⁺-3 $$ orbitals in a square planar geometry. Resonant inelastic X-ray scattering measurements reveal sharp magnon excitations of 200 meV energy at the magnetic Brillouin zone boundary, highly resonant at the Ni^{1 +} absorption peak. The results indicate that, when properly stabilized, infinite-layer nickelate thin films are superconducting without chemical doping.