Robust Superconductivity in Infinite-Layer Nickelates.

The recent discovery of nickelate superconductivity represents an important step toward understanding the four-decade mastery of unconventional high-temperature superconductivity. However, the synthesis of the infinite-layer nickelate superconductors shows great challenges. Particularly, surface capping layers are usually unitized to facilitate the sample synthesis. This leads to an important question whether nickelate superconductors with d 9 configuration and ultralow valence of Ni 1+ are in metastable state and whether nickelate superconductivity can be robust? In this work, a series of redox cycling experiments are performed across the phase transition between perovskite Nd 0.8 Sr 0.2 NiO 3 and infinite-layer Nd 0.8 Sr 0.2 NiO 2 . The infinite-layer Nd 0.8 Sr 0.2 NiO 2 is quite robust in the redox environment and can survive the cycling experiments with unchanged crystallographic quality. However, as the cycling number goes on, the perovskite Nd 0.8 Sr 0.2 NiO 3 shows structural degradation, suggesting stability of nickelate superconductivity is not restricted by the ultralow valence of Ni 1+ , but by the quality of its perovskite precursor. The observed robustness of infinite-layer Nd 0.8 Sr 0.2 NiO 2 up to ten redox cycles further indicates that if an ideal high-quality perovskite precursor can be obtained, infinite-layer nickelate superconductivity can be very stable and sustainable under environmental conditions. This work provides important implications for potential device applications for nickelate superconductors.