Robust Superconductivity in Infinite-Layer Nickelates

Abstract

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 Nd_0.8Sr_0.2NiO₃ and infinite-layer Nd_0.8Sr_0.2NiO₂. The infinite-layer Nd_0.8Sr_0.2NiO₂ 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 Nd_0.8Sr_0.2NiO₃ 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 Nd_0.8Sr_0.2NiO₂ 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.

Keywords: nickelates; reversible; superconductor; topological relationships.