Superconductivity in an infinite-layer nickelate.

The discovery of unconventional superconductivity in (La,Ba) ₂ CuO ₄ (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 Sr ₂ RuO ₄ (ref. ² ) and surface-electron-doped Sr ₂ IrO ₄ , 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 LaAlO ₃ /LaNiO ₃ superlattice ^7-9 , which has been recently proposed for the creation of an artificially layered nickelate heterostructure with a singly occupied [Formula: see text] band. The absence of superconductivity observed in previous related experiments has been attributed, at least in part, to incomplete polarization of the e _g orbitals ¹⁰ . 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 , NdNiO ₂ and Nd _0.8 Sr _0.2 NiO ₂ single-crystal thin films are synthesized by reducing the perovskite precursor phase. Whereas NdNiO ₂ exhibits a resistive upturn at low temperature, measurements of the resistivity, critical current density and magnetic-field response of Nd _0.8 Sr _0.2 NiO ₂ 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 oxides ²⁴ and pnictides ²⁵ .