CAREER: Nonlinear THz electrodynamics of spin quasiparticles

职业：自旋准粒子的非线性太赫兹电动力学

• 批准号: 2144256
• 负责人: Fahad Mahmood
• 金额: $ 58.67万
• 依托单位: University of Illinois at Urbana-Champaign
• 依托单位国家: 美国
• 项目类别: Continuing Grant
• 财政年份: 2022
• 资助国家: 美国
• 起止时间: 2022-05-01 至 2027-04-30
• 项目状态: 未结题
• 来源: https://www.nsf.gov/awardsearch/showAward?AWD_ID=2144256&HistoricalAwards=false
• 关键词: CAREER; Nonlinear; THz; electrodynamics; spin

This award is funded in whole or in part under the American Rescue Plan Act of 2021 (Public Law 117-2). Nontechnical abstract:Nearly all existing computing devices are based on the manipulation of the charge of electrons. Unfortunately, fundamental limits at which charge information can be transmitted and preserved is slowing down and preventing breakthrough technological advances in next-generation computing. Recent research has indicated that this impasse can be overcome by using the collective motion of the spin of electrons. The spin of an electron is like a microscopic bar magnet. Most magnetic materials can be thought of as consisting of these tiny electron magnets aligned and fixed in a geometric pattern. In certain materials, however, the quantum interactions between these electron magnets causes them to move synchronously rather than remaining aligned. These collective behaviors are called emergent spin quasiparticles, and they are predicted to have the unique ability to store and transmit information in the form of angular momentum while not carrying any electron charge. In this way, spin quasiparticles can potentially enable faster, more energy-efficient and robust computation than is currently possible. However, these particles are hard to detect, and the underlying rules governing their behavior are poorly understood. This research project fills this knowledge gap by developing experimental methods based on powerful light sources to directly observe and manipulate these spin quasiparticles. Simultaneously, the educational component of this project increases exposure of middle school students to modern physics concepts (such as quantum mechanics) through a traveling and interactive physics demonstration show called the “Physics Van.” Undergraduate students at the University of Illinois are also coached as part of this project to lead these demos, visit local schools, and mentor middle school students on viable future pathways into science and engineering fields.This project is jointly funded by the Condensed Matter Physics (CMP) and the Electronic and Photonic Materials (EPM) programs of the Division of Materials Research (DMR).Technical abstract: In a variety of magnetic insulators, strong interactions, geometric frustration, and low dimensionality intertwine to give emergent spin quasiparticles that can be viable platforms for quantum computation and efficient spintronics. Examples include fractionalized spin excitations (spinons) and antiferromagnetic magnon currents. This experimental project uses nonlinear optical response in the terahertz (THz) range to measure, characterize and ultimately manipulate these spin quasiparticles. The specific objectives are (1) identifying distinctive experimental signatures of spinons in the nonlinear THz susceptibility of quantum magnets as indicated by recent theoretical work; (2) driving coherent antiferromagnet currents in insulators using strong THz light-spin coupling; and (3) understanding decoherence and relaxation mechanisms of THz-induced spin excitations. The research effort is implemented by using newly developed multidimensional nonlinear THz spectroscopies on magnetic heterostructures having resonators specifically designed to enhance THz light-matter coupling. This approach allows highly controllable and adaptable settings for inducing the strongest possible light-matter coupling. Materials under study include two-dimensional quantum spin liquid candidates, one-dimensional spin chains that are known to host spinons, and trivial antiferromagnetic insulators. The nonlinear magnetic susceptibility and shift magnon currents in these materials is measured to systematically determine relaxation and decoherence properties of spin quasiparticles. This work establishes a framework for discovering new spin quasiparticles and implements nonlinear THz spectroscopy as a general method to probe material properties inaccessible in conventional linear spectroscopies.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.

该奖项全部或部分由《2021 年美国救援计划法案》（公法 117-2）资助。不幸的是，几乎所有现有的计算设备都基于电子电荷的操纵。电荷信息的传输和保存正在减慢并阻碍下一代计算的突破性技术进步。最近的研究表明，可以通过使用电子自旋的集体运动来克服这种僵局。大多数磁性材料可以被认为是由这些以几何图案排列和固定的微小电子磁体组成，但是在某些材料中，这些电子磁体之间的量子相互作用导致它们同步移动而不是保持排列。这些集体行为被称为涌现自旋准粒子，预计它们具有以角动量形式存储和传输信息的独特能力，同时不携带任何电子电荷，这样，自旋准粒子就有可能实现更快、更多的能量。高效且然而，这些粒子很难被检测到，并且人们对控制它们行为的基本规则知之甚少，该研究项目通过开发基于强大光源的实验方法来直接观察和操纵这些自旋，从而填补了这一知识空白。同时，该项目的教育部分还通过名为“物理范”的巡回互动物理演示节目增加了中学生对现代物理概念（例如量子力学）的接触。作为其中的一部分接受指导项目的目的是领导这些演示，参观当地学校，并指导中学生未来进入科学和工程领域的可行途径。该项目由凝聚态物理（CMP）和电子和光子材料（EPM）项目共同资助材料研究部（DMR）。技术摘要：在各种磁绝缘体中，强相互作用、几何挫败和低维交织在一起，产生了新兴的自旋准粒子，这些粒子可以成为量子计算和高效的可行平台自旋电子学的例子包括分段自旋激发（自旋子）和反铁磁磁振子电流。该实验项目使用太赫兹（THz）范围内的非线性光学响应来测量、表征并最终操纵这些自旋准粒子。最近的理论工作表明，量子磁体的非线性太赫兹磁化率中的自旋子特征；（2）驱动绝缘体中的相干反铁磁体电流；使用强太赫兹光自旋耦合；（3）了解太赫兹诱导自旋激发的退相干和弛豫机制该研究工作是通过使用新开发的多维非线性太赫兹光谱来实现的，该磁异质结构具有专门设计用于增强太赫兹光物质的谐振器。这种方法允许高度可控和适应性强的设置，以诱导最强的光-物质耦合。正在研究的材料包括二维量子自旋液体候选物、已知的一维自旋链。测量这些材料中的非线性磁化率和位移磁振子电流，以任意确定自旋准粒子的弛豫和退相干特性，并建立了一个发现新自旋准粒子的框架，并实现了非线性太赫兹光谱。探测传统线性光谱无法获得的材料特性的方法。该奖项反映了 NSF 的法定使命，并被认为值得支持通过使用基金会的智力优点和更广泛的影响审查标准进行评估。