CAREER: Anomalous spin dynamics in triangular quantum magnets: from materials discovery to quantitative neutron spectroscopy

非技术：磁现象对量子材料革命至关重要。自旋之间复杂的相互作用——由束缚在晶格上的电子携带的量子化的“罗盘针”——为磁性物质提供了理想的量子相干性。例如，一种被称为“量子自旋液体”的特殊物质状态可以用于新的量子信息和传感技术。然而，这些奇怪的新量子态涉及许多自旋，在实际材料中预测和测量都极具挑战性。这项实验研究汇集了材料科学、光谱学和建模，以发现宏观量子效应是否以及如何在相互作用的自旋网络中出现。该项目专注于一组未开发的无机化合物，这些化合物是为新型行为而设计的。这项研究将利用中子光谱学来精确地绘制定制样品中的自旋态，从而直接从现实的理论模型中进行预测。该项目的专业研究人员将与高中生、他们的老师和本科生合作，产生对材料研究的长期兴趣，并提供支持未来量子劳动力所需的网络。参与者不仅在首席研究员的实验室里接受样品生长和低温测量方面的培训，而且还参与了世界级的晶体生长和中子散射实验，例如在橡树岭国家实验室。随后，参与者与普通大众和大学公众接触，揭露凝聚态物质中的“宇宙”之美，并传达量子材料革命的承诺。技术摘要：相关磁绝缘体是当前量子革命核心的独特材料。它们经常为一个普遍的问题提供明确的答案：宏观量子现象是如何从原子尺度实体的集合中出现在晶体物质中的？一些相互作用的自旋系统拥有理想的量子相，而没有经典的类似物——其特征是高度纠缠，它们的激发是非局域的，像自旋子或马约拉纳费米子。然而，在大多数情况下，这些多体状态很难用现有的技术来预测。因此，在真实材料中实现和检测真正的量子相是极具挑战性的。这项实验研究将内部努力与美国世界级的晶体生长和非弹性中子散射中心相结合，以跟踪和揭示相互作用自旋三角形网络中的量子现象。低维和几何受挫的三角晶格反铁磁体处于半经典和量子行为之间的边界。这种趋势，当结合自旋空间各向异性和由成分变化调谐的量子涨落时，产生新的相和准粒子。研究活动推进了非弹性中子散射仪器和数据分析工具，以准确地绘制实验室生长样品中的自旋激发，并从现实模型中进行基准预测。三个相关的研究方向是：(1)过渡金属化合物中磁振子准粒子的非线性动力学和可能的击穿；(2)稀土磁体的自旋-轨道诱导各向异性和自旋-液体现象学；(3)新型三角晶格材料的发现与表征。由高中生、本科生和研究生组成的团队在首席研究员的实验室和大型中心设施中参与研究过程的每一步。由专业研究人员对参与者进行指导，为支持未来的量子劳动力提供了所需的脚手架。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。

Non-Technical: Magnetic phenomena are essential to the quantum materials revolution. Complex interactions between spins - quantized "compass needles" carried by electrons bound to crystal lattices - provide magnetic matter with desirable quantum coherence properties. For instance, a special state of matter called a "quantum spin-liquids" could be used for new quantum information and sensing technologies. However, these strange new quantum states involve many spins and are incredibly challenging to both predict and measure in real materials. This experimental research brings together materials science, spectroscopy, and modeling to discover if and how macroscopic quantum effects emerge in networks of interacting spins. The project focuses on an unexplored set of inorganic compounds that are designed for new types of behavior. This research will utilize neutron spectroscopy to accurately map spin states in custom-grown samples and so, probe directly predictions from realistic theoretical models. Professional researchers in the project will team with high-school students, their teachers, and undergraduate students to generate a long-lasting interest for materials research and provide the network needed to support the future quantum workforce. Participants not only train in sample growth and cryogenic measurements in the principal investigator's laboratory, but also get involved in experiments at world-class facilities for crystal growth and neutron scattering, for instance at Oak Ridge National Laboratory. Participants subsequently engage the general and university public to expose the beauty of "the Universe" within condensed matter and communicate the promise of the quantum materials revolution.Technical Abstract: Correlated magnetic insulators are unique materials at the heart of the current quantum revolution. They often provide definitive answers to a universal question: how do macroscopic quantum phenomena emerge in crystalline matter from assemblies of atomic-scale entities? Several systems of interacting spins host desirable quantum phases with no classical analogues - characterized by a high degree of entanglement, their excitations are non-local like spinons or Majorana fermions. In most cases, however, these many-body states are difficult to predict with existing techniques. Realizing and detecting genuine quantum phases in real materials is therefore extremely challenging. This experimental research merges in-house efforts with the use of world-class centers for crystal growth and inelastic neutron-scattering in the United States to track and expose quantum phenomena in triangular networks of interacting spins. Low-dimensional and geometrically frustrated, triangular-lattice antiferromagnets are at the boundary between semi-classical and quantum behaviors. This tendency, when combined with spin-space anisotropies and quantum fluctuations tuned by compositional variations, produces novel phases and quasiparticles. The research activities advance inelastic neutron scattering instrumentation and data analysis tools to accurately map spin excitations in laboratory-grown samples and to benchmark predictions from realistic models. Three related directions are explored: (1) nonlinear dynamics and possible breakdown of magnon quasiparticles in transition-metal compounds; (2) spin-orbit-induced anisotropies and spin-liquid phenomenology in rare-earth magnets; (3) discovery and characterization of new triangular-lattice materials. Teams of high-school, undergraduate and graduate students participate in every step of the research process in the principal investigator's laboratory and at large-scale central facilities. Mentoring of participants by professional researchers provides the scaffolding needed to support the future quantum workforce.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.