Stanford Institute for Materials and Energy Sciences, SLAC National Accelerator Laboratory, Menlo Park, CA, USA.
Department of Applied Physics, Stanford University, Stanford, CA, USA.
Nature. 2019 Aug;572(7771):624-627. doi: 10.1038/s41586-019-1496-5. Epub 2019 Aug 28.
The discovery of unconventional superconductivity in (La,Ba)CuO (ref. ) 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 SrRuO (ref. ) and surface-electron-doped SrIrO, which exhibits spectroscopic signatures consistent with a superconducting gap, although a zero-resistance state has not yet been observed. This approach has also led to the theoretical investigation of nickelates, as well as thin-film heterostructures designed to host superconductivity. One such structure is the LaAlO/LaNiO superlattice, 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 orbitals. Here we report the observation of superconductivity in an infinite-layer nickelate that is isostructural to infinite-layer copper oxides. Using soft-chemistry topotactic reduction, NdNiO and NdSrNiO single-crystal thin films are synthesized by reducing the perovskite precursor phase. Whereas NdNiO exhibits a resistive upturn at low temperature, measurements of the resistivity, critical current density and magnetic-field response of NdSrNiO 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, these results suggest the possibility of a family of nickelate superconductors analogous to copper oxides and pnictides.
在（La,Ba）CuO 中发现非常规超导性（参考文献）激发了对具有相似晶体和电子结构的化合物的研究，目的是寻找额外的超导体并理解铜氧化物超导性的起源。同构的例子包括块状超导 SrRuO（参考文献）和表面电子掺杂的 SrIrO，其表现出与超导能隙一致的光谱特征，尽管尚未观察到零电阻状态。这种方法还导致了对镍酸盐的理论研究，以及旨在承载超导性的薄膜异质结构。这种结构之一是 LaAlO/LaNiO 超晶格，最近有人提出这种结构是为了创建具有单个占据 [Formula: see text] 带的人工层状镍酸盐异质结构。以前相关实验中观察到的缺乏超导性至少部分归因于 e 轨道的不完全极化。在这里，我们报告了在与无限层铜氧化物同构的无限层镍酸盐中观察到的超导性。通过软化学拓扑还原，通过还原钙钛矿前体相合成 NdNiO 和 NdSrNiO 单晶薄膜。虽然 NdNiO 在低温下表现出电阻上升，但 NdSrNiO 的电阻率、临界电流密度和磁场响应测量表明超导转变温度约为 9 到 15 开尔文。由于该化合物是一系列还原的层状镍酸盐晶体结构的成员，这些结果表明存在一系列类似于铜氧化物和磷化物的镍酸盐超导体的可能性。
