Superconductivity in an infinite-layer nickelate

The discovery of unconventional superconductivity in (La,Ba)₂CuO₄ (ref. ¹) has motivated the study of compounds with similar crystal and electronic structure, with the aim of finding additional superconductors and understanding the origins of copper oxide superconductivity. Isostructural examples include bulk superconducting Sr₂RuO₄ (ref. ²) and surface-electron-doped Sr₂IrO₄, which exhibits spectroscopic signatures consistent with a superconducting gap^3,4, although a zero-resistance state has not yet been observed. This approach has also led to the theoretical investigation of nickelates^5,6, as well as thin-film heterostructures designed to host superconductivity. One such structure is the LaAlO₃/LaNiO₃ superlattice^7-9, which has been recently proposed for the creation of an artificially layered nickelate heterostructure with a singly occupied d_x²-y² band. The absence of superconductivity observed in previous related experiments has been attributed, at least in part, to incomplete polarization of the e_g orbitals¹⁰. Here we report the observation of superconductivity in an infinite-layer nickelate that is isostructural to infinite-layer copper oxides^11-13. Using soft-chemistry topotactic reduction^14-20, NdNiO₂ and Nd_0.8Sr_0.2NiO₂ single-crystal thin films are synthesized by reducing the perovskite precursor phase. Whereas NdNiO₂ exhibits a resistive upturn at low temperature, measurements of the resistivity, critical current density and magnetic-field response of Nd_0.8Sr_0.2NiO₂ indicate a superconducting transition temperature of about 9 to 15 kelvin. Because this compound is a member of a series of reduced layered nickelate crystal structures^21-23, these results suggest the possibility of a family of nickelate superconductors analogous to copper oxides²⁴ and pnictides²⁵.