Quenched Disorder in Frustrated Magnets

该奖项支持磁性材料特性的理论和计算建模的研究和教育，其中量子力学起着核心作用。磁性是一种与电子微小的固有磁矩（称为自旋）有关的现象。在最著名的磁性材料中，如铁，材料中的电子自旋彼此平行排列，并在宏观尺度上产生磁场。我们通过它们的磁力来体验这些。在另一类磁性材料中，自旋与相邻的自旋反平行排列。这种材料不表现出宏观磁力，但它们的行为仍然可以在经典框架内理解。在磁性的背景下，挫折是一个技术术语，表示在微观层面上竞争力量的存在。挫折可以破坏任何自旋顺序的安排，并导致更复杂的行为。量子力学对于描述这种磁相是必不可少的。具有这些磁相的材料可以容纳新型粒子，并对温度变化、电流或电磁场表现出新型的响应。它们可以为新一代量子设备提供平台。近年来，许多这样的量子磁性材料已经被合成并正在研究中。然而，真正的材料总是带有缺陷或杂质。这些杂质有时会降解，有时会稳定外来性质。该项目旨在详细了解杂质在磁性受挫中的作用。这些研究除了对理解奇异量子材料和技术具有科学价值外，还为本科生和研究生提供了理论和计算方法方面的良好培训。技术总结：该奖项支持研究和教育的作用淬火无序的挫折磁铁使用理论和计算方法。对物质的奇异量子自旋液相的探索正处于一个有趣的关头。已经合成了几个磁性材料族，它们表现出缺乏传统的磁性秩序。我们已经建立了一个理论框架来理解物质的量子自旋液相，其中包括精确可解模型和涌现规范理论。与此同时，计算方法已经开发出来，可以解决研究这种材料的定量宏观特性所需的现实量子自旋模型。本项目将通过一些理论和计算技术来解决这种具有淬火杂质的量子自旋模型。这些技术包括PI和他的团队开发的级数展开和数值链接簇展开。通过计算熵和比热等热力学性质，自旋电流和自旋扩散等动力学性质，以及各种响应和散射性质，为输运、中子散射和核磁共振实验等各种实验研究提供定量支持。这些研究应该有助于全面了解这类材料，并为它们在下一代量子技术中的可能应用做好准备。这些研究除了对理解奇异量子材料和技术具有科学价值外，还为本科生和研究生提供了理论和计算方法方面的良好培训。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 SUMMARYThis award supports research and education on theoretical and computational modeling of the properties of magnetic materials, where quantum mechanics plays a central role. Magnetism is a phenomenon associated with the electron's tiny intrinsic magnetic moment, called spin. In the best-known magnetic materials, such as iron, electrons in the material have their spins lined up parallel to each other and produce magnetic fields at macroscopic scales. We experience these through their magnetic forces. In another class of magnetic materials, spins line up anti-parallel with their neighbors. Such materials do not exhibit macroscopic magnetic forces, but their behavior can still be understood within a classical framework. Frustration in the context of magnetism is a technical term that denotes the existence of competing forces at the microscopic level. Frustration can destabilize any arrangement of spin order and lead to far more complex behavior. Quantum mechanics is essential for describing such magnetic phases. Materials having these magnetic phases can harbor new types of particles and show new types of responses to temperature changes, electric current, or electromagnetic fields. They could provide platforms for a new generation of quantum devices. In recent years, many such quantum magnetic materials have been synthesized and are being studied. However, real materials always come with imperfections or impurities. Such impurities can sometimes degrade and sometimes stabilize exotic properties. This project seeks to understand in detail the role of impurities in frustrated magnetism.In addition to their scientific value to the understanding of exotic quantum materials and technologies, these studies also provide excellent training ground for undergraduate and graduate students in theoretical and computational methods.TECHNICAL SUMMARYThis award supports research and education on the role of quenched disorder in frustrated magnets using theoretical and computational methods. The quest for exotic quantum spin-liquid phases of matter is poised at an interesting juncture. Several families of magnetic materials have been synthesized that exhibit absence of conventional magnetic order. A theoretical framework is in place for understanding quantum spin-liquid phases of matter that includes exactly solvable models and emergent gauge theories. In parallel, computational methods have been developed that can address realistic quantum spin models needed to study quantitative macroscopic properties of such materials. This project will address such quantum spin models with quenched impurities by a number of theoretical and computational techniques. These techniques include series expansions and numerical linked cluster expansions developed by the PI and his group. By calculating thermodynamic properties such as entropy and specific heat, dynamical properties such as spin-currents and spin-diffusion, and various response and scattering properties, the work should provide quantitative support to various experimental studies including transport, neutron scattering and NMR experiments. These studies should help develop a comprehensive understanding of these class of materials and prepare them for their possible use in next-generation quantum technologies.In addition to their scientific value to the understanding of exotic quantum materials and technologies, these studies also provide excellent training ground for undergraduate and graduate students in theoretical and computational methods.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.