Synthesis and Spectroscopy of Thin Film Nickelate Superconductors

材料的电子性质对现代文明和社会至关重要，使电信，计算和信息存储和处理等技术成为可能。在这些性质中，超导性在量子信息处理和通信、医学成像、能量存储和传输以及电子学中的应用特别有前途。发现和设计具有上级性能的新超导体的可能性，例如更高的工作温度或更大的电流密度，是现代物理学的前沿之一。该项目的目标是通过调查新发现的但仍然神秘的基于氧化镍的超导体家族，并将这些材料与密切相关且更完善的氧化铜高温超导体家族进行比较，对长期存在的高温超导性难题提供更连贯和全球性的理解。通过更好地了解这些氧化镍超导体，并将它们的性质与氧化铜表兄弟进行比较，该项目可以解开发现高温超导体的关键成分。最后，该项目为年轻科学家提供了材料合成和表征、外联活动方面的重要培训，这些研究中制作的样品支持了全国各地的几项科学合作。技术摘要：Ni 1+价态的层状镍酸盐长期以来一直被认为是铜酸盐和另一个潜在的高温超导体家族的密切电子类似物。最近在无限层状结构中掺杂稀土镍酸盐在15 K下的超导性的发现引发了人们对这些材料的浓厚兴趣，但是关于这些化合物还有许多悬而未决的问题，包括超导性的性质，它们的基本电子结构，以及哪些方面与铜酸盐相似或不同。这个项目的目标是合成和研究无限层镍酸盐的薄膜，使用氧化物分子束外延和角分辨光电子能谱的组合来解决镍酸盐的基本问题，包括超导间隙的动量依赖性，赝隙的存在和性质，母体化合物的电子结构和正常态的电子结构。这里提出的研究包括两个主要阶段，特别是无限层镍酸盐薄膜的合成，从氧化物MBE合成前体钙钛矿镍酸盐开始，然后还原以实现无限层结构。接下来，角分辨光电子能谱解决了这些镍酸盐超导体的关键问题，包括超导序参量的性质，母体化合物的电子结构，空穴掺杂到超导状态的电子结构的演变，以及可能存在的赝能隙。通过该项目合成的样品支持了大量的外部合作，包括光学光谱和磁成像。该奖项反映了NSF的法定使命，并通过使用基金会的知识价值和更广泛的影响审查标准进行评估，被认为值得支持。

Nontechnical Abstract:The electronic properties of materials are critical to modern civilization and society, enabling technologies such as telecommunications, computing, and information storage and processing. Among these properties, superconductivity is particularly promising for applications in quantum information processing and communication, medical imaging, energy storage and transport, and electronics. The possibility to discover and engineer new superconductors with superior properties, such as higher operating temperatures or larger current densities, is one of the frontiers of modern physics. The objective of this project is to provide a more coherent and global understanding of the long-standing puzzle of high-temperature superconductivity through the investigation of a newly discovered but still enigmatic family of superconductors based on nickel oxides and comparing these materials to the closely related and more well-established family of copper oxide high-temperature superconductors. By achieving a better understanding of these nickel oxide superconductors and comparing their properties with their copper oxide cousins, this project could unlock the key ingredients for discovering higher temperature superconductors. Finally, this project provides crucial training to young scientists in materials synthesis and characterization, outreach activities, and the samples fabricated in these studies supports several scientific collaborations across the country. Technical Abstract:Layered nickelates with a Ni 1+ valence have long been proposed as close electronic analogues to the cuprates and another potential family of high temperature superconductors. The recent discovery of superconductivity at 15 K in doped rare earth nickelates in the infinite layer structure has ignited intense interest in these materials, but there are many open questions about these compounds, including the nature of the superconductivity, their underlying electronic structure, and which aspects are similar or different from the cuprates. The objectives of this project are to synthesize and investigate thin films of infinite layer nickelates using a combination of oxide molecular beam epitaxy and angle-resolved photoemission spectroscopy to address fundamental questions about the nickelates, including the momentum-dependence of the superconducting gap, the presence and nature of a pseudogap, the electronic structure of the parent compounds, and the normal state electronic structure. The research proposed here consists of two primary stages, specifically the synthesis of infinite-layer nickelate thin films, beginning with oxide MBE synthesis of precursor perovskite nickelates, followed by reduction to achieve the infinite layer structure. Next, angle-resolved photoemission spectroscopy addresses crucial questions about these nickelate superconductors, including the nature of the superconducting order parameter, the electronic structure of the parent compound, the evolution of the electronic structure with hole doping into the superconducting state, and the possible existence of a pseudogap. The samples synthesized through this project support a wide number of external collaborations, including optical spectroscopy and magnetic imaging.This award reflects NSF's statutory mission and has been deemed worthy of support through evaluation using the Foundation's intellectual merit and broader impacts review criteria.