NMR Studies of Nematicity in Strongly Correlated Electron Systems under Uniaxial Strain

摘要：在高温超导体中，低温时会出现零电阻的电子态。超导是一种量子力学现象，具有广泛的潜在应用，包括磁悬浮和无耗散能量传输，能够以变革性的方式改变社会和经济。但是人们对超导性的了解仍然很少，并且在各种类型的材料中都能看到。一个特别有趣的情况发生在向列材料中，其中电子行为自发地变成各向异性。这种行为可以在实验室中通过对晶体施加应变来诱导，这可能会改变其物理性质。我们的目的是研究微观行为的磁共振研究电子响应应变。该项目将通过大学推广办公室为公众开设一门新的无方程量子力学课程，支持本科生和研究生以及广大老年人的教育。技术摘要：本项目的目标是发展对强相关电子材料的量子临界向列波动的基本理解。在铁和铜超导体中观察到电子向列序，有证据表明，向列波动可能是超导配对机制和这些材料中最佳掺杂时非费米液体行为的原因。然而，多种类型的有序参数及其波动的存在使实验的解释复杂化，并排除了识别这些现象背后的基本物理。最近的证据表明，在某些情况下，电子向列波动可能是超导性的原因。然而，多种类型的电子有序参数可以同时存在，并且由于它们的本质，强相关系统对杂质高度敏感，导致微观不均匀性，从而混淆实验观察。因此，电子向列性在多大程度上是铁和铜酸盐材料高温超导的基础物理的核心，或者它是否仅仅是一种奇怪的附带现象，目前还没有明确的描述。该项目将通过核磁共振研究铜酸盐、钒酸盐、铱酸盐和镍酸铁材料在从未被研究过的相空间体制下的单轴应变来回答这个问题。这些研究将解开在高温铁和铜超导体正常状态下无序、向列性和反铁磁性的作用，并将利用单轴应变作为热力学调谐变量探索相空间的新体制。该项目的结果将是更全面地了解量子临界向列波动的作用和强相关电子材料的基本物理。该奖项反映了美国国家科学基金会的法定使命，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: In high temperature superconductors an electronic state with zero resistance emerges at low temperatures. Superconductivity is a quantum mechanical phenomenon that has a wide range of potential applications, including magnetic levitation and energy transport without dissipation, capable of changing the society and economy in a transformative way. But superconductivity is still poorly understood and is seen in various types of materials. A particularly interesting case occurs for nematic materials, in which the electronic behavior spontaneously becomes anisotropic. This behavior can be induced in the laboratory by applying strain to the crystal, which may alter its physical properties. We aim to investigate the microscopic behavior using magnetic resonance to study the electronic response to strain. This project will support the education of undergraduate and graduate students, as well as a broad audience of senior citizens via a new course on quantum mechanics without equations for the public through the university extension office. Technical Abstract: The objective of this project is to develop a fundamental understanding of quantum critical nematic fluctuations in strongly correlated electron materials. Electronic nematic order has been observed in the iron and cuprate superconductors, and evidence suggests that nematic fluctuations may be responsible for the superconducting pairing mechanism and the non-Fermi liquid behavior at optimal doping in these materials. However, the presence of multiple types of order parameters and their fluctuations complicate the interpretation of experiments and preclude the identification of the essential physics behind these phenomena. Recent evidence suggests that electronic nematic fluctuations may be responsible for superconductivity in some cases. However, multiple types of electronic order parameters can be present simultaneously, and by their very nature strongly correlated systems are highly sensitive to impurities, giving rise to microscopic inhomogeneity that obfuscates experimental observations. As a result, there is no clear picture as to what extent electron nematicity is central to the fundamental physics of high temperature superconductivity in the iron and cuprates materials, or whether it is simply a curious epiphenomenon. This project will answer this question through nuclear magnetic resonance studies of cuprates, vanadates, iridates and iron pnictide materials under uniaxial strain in regimes of phase space that have never been investigated. These investigations will disentangle the roles of disorder, nematicity, and antiferromagnetism at play in the normal state of the high temperature iron and cuprate superconductors, and will also explore new regimes of phase space using uniaxial strain as a thermodynamic tuning variable. The outcome of this project will be a more complete understanding of the role of quantum critical nematic fluctuations and the essential physics of strongly correlated electron materials.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.