发表机构
Argonne National Laboratory; University of Illinois Chicago; School of Physics, Southeast University; Norfolk State University（阿贡国家实验室; 伊利诺伊大学芝加哥分校; 东南大学物理学院; 诺福克州立大学）
机构由 AI 辅助整理，请以论文原文为准。AI 中文总结
本研究在常压块体镍酸盐单晶中发现超导电性，其出现在金属-绝缘体相边界附近，并揭示间隔层体积是调控电子相图的关键参数，为探索镍酸盐超导电性提供了新途径。
AI 中文摘要
镍酸盐中超导电性的发现开创了在过渡金属氧化物中探索非常规超导电性的新领域。然而，迄今为止，超导电性仅在薄膜中或在块体材料的极端压力下得以实现。在此，我们报道了在常压下块体镍酸盐单晶(La1-xPrx)4Ni3O8和(La1-xYx)4Ni3O8中观测到的超导电性迹象，其晶体结构由方平面氧化镍三层与萤石状间隔层交错排列而成。母体化合物La4Ni3O8呈现绝缘基态，其中电子有序排列成交织的绝缘电荷/自旋条纹。较小镧系离子的替代破坏了这种有序，最终导致金属基态。我们发现超导电性出现在邻近绝缘体-金属相边界的狭窄窗口内，在此窗口中金属相和电荷条纹相共存。观测到的低体积分数超导电性是非逾渗性的，表明存在在这些相边界处成核的丝状超导电性的可能性。然而，在透射电子显微镜中观测到近似已知无限层镍酸盐的共生缺陷，这留下了超导电性可能存在于此处而非三层基质中的可能性。值得注意的是，当以萤石状间隔层的体积为参数时，Y系和Pr系两者的电子相图重合，揭示出这一空间位阻参数深刻修饰了氧化镍三层的电子结构。我们的结果确定，更好地理解金属相与电荷有序相之间的共存区域是扩大块体常压镍酸盐超导电性范围的首要任务，并确立了间隔层工程作为探索这一相竞争区域的的设计工具。
英文摘要
The discovery of superconductivity in nickelates has seeded a new field for exploring unconventional superconductivity in transition metal oxides. However, to date superconductivity has only been realized in thin films or under extreme pressure in the bulk. Here we report signatures of superconductivity at ambient pressure in bulk nickelate single crystals of (La1-xPrx)4Ni3O8 and (La1-xYx)4Ni3O8, whose crystal structure comprises interleaving trilayers of square-planar nickel oxide and fluorite-like spacer layers. The parent compound La4Ni3O8 exhibits an insulating ground state, where electrons order into intertwined, insulating charge/spin stripes. Substitution of smaller lanthanide ions disrupts this order, eventually leading to a metallic ground-state. We find that superconductivity emerges in a narrow window proximate to the insulator-metal phase boundary, where both metallic and charge-stripe phases co-exist. The observed low volume-fraction superconductivity is non-percolative, suggesting the prospect of filamentary superconductivity nucleated at the boundary between these phases. However, intergrowth defects that approximate the known infinite layer nickelates are observed in TEM, leaving open the possibility that superconductivity resides here rather than in the trilayer matrix. Remarkably, the electronic phase diagrams of both the Y and Pr series coincide when parameterized by the volume of the fluorite like spacer layers, revealing that this steric parameter profoundly modifies the nickel oxide trilayer electronic structure. Our results identify better understanding of the co-existence region between metallic and charge-ordered phases as a priority for expanding the range of bulk, ambient-pressure nickelate superconductivity and establish spacer-layer engineering as a design tool for exploring this regime of phase competition.
