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 d9 configuration and ultralow valence of Ni1+ 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 Nd0.8Sr0.2NiO3 and infinite-layer Nd0.8Sr0.2NiO2. The infinite-layer Nd0.8Sr0.2NiO2 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 Nd0.8Sr0.2NiO3 shows structural degradation, suggesting stability of nickelate superconductivity is not restricted by the ultralow valence of Ni1+, but by the quality of its perovskite precursor. The observed robustness of infinite-layer Nd0.8Sr0.2NiO2 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. The infinite-layer structure is achieved by deintercalation of apical oxygens of perovskite nickelates, forming alternating planer [NiO2] layers and [Nd0.8Sr0.2] space layers. Therefore, it is important to give a comprehensive understanding of oxygen evolution in space layers and its impact on nickelate superconductivity. A reversible transition is demonstrated between the perovskite Nd0.8Sr0.2NiO3 and the infinite-layer Nd0.8Sr0.2NiO2 thin films without losing their structural framework and topological relationships. The superconductivity in Nd0.8Sr0.2NiO2 still exists even for ten times of "deintercalation-intercalation" cycles, indicating the robustness of the infinite-layer structural frame. image