Quenched Disorder in Frustrated Magnets

受挫磁铁中的淬灭无序

• 批准号: 1855111
• 负责人: Rajiv Singh
• 金额: $ 31.48万
• 依托单位: University of California-Davis
• 依托单位国家: 美国
• 项目类别: Continuing Grant
• 财政年份: 2019
• 资助国家: 美国
• 起止时间: 2019-07-01 至 2023-09-30
• 项目状态: 已结题
• 来源: https://www.nsf.gov/awardsearch/showAward?AWD_ID=1855111&HistoricalAwards=false
• 关键词: Quenched; Disorder; Frustrated; Magnets

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.

非技术总结该奖项支持磁性材料性质的理论和计算建模方面的研究和教育，其中量子力学起着核心作用。磁性是一种与电子微小的内部磁矩有关的现象，称为自旋。在最著名的磁性材料中，如铁，材料中的电子具有相互平行的自旋，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，自旋与邻近的自旋反平行排列。这种材料不会表现出宏观的磁力，但它们的行为仍然可以在经典框架内得到理解。在磁性的背景下，挫折是一个技术术语，表示微观层面上存在相互竞争的力量。挫折感可能会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样的磁相是必不可少的。具有这些磁性相的材料可以容纳新类型的粒子，并对温度变化、电流或电磁场显示出新类型的响应。它们可以为新一代量子设备提供平台。近年来，已经合成了许多这样的量子磁性材料，并正在进行研究。然而，真正的材料总是伴随着瑕疵或杂质。这类杂质有时会降低稀有特性，有时会使其稳定。本项目旨在详细了解杂质在受挫磁体中的作用。除了它们对理解奇异量子材料和技术的科学价值外，这些研究还为本科生和研究生提供了极好的理论和计算方法培训基础。技术总结该奖项支持使用理论和计算方法研究和教育淬火无序在受挫磁体中的作用。对物质的奇异量子自旋-液体相的探索正处于一个有趣的关头。人们已经合成了几个系列的磁性材料，它们没有传统的磁序。一个理论框架已经到位，用于理解物质的量子自旋-液体相，其中包括精确可解的模型和浮现规范理论。与此同时，已经开发了一些计算方法，可以解决研究此类材料的定量宏观性质所需的真实量子自旋模型。这个项目将通过一些理论和计算技术来解决这类带有猝灭杂质的量子自旋模型。这些技术包括由PI和他的团队开发的级数展开和数值链接的团簇展开。通过计算热力学性质，如熵和比热，动力学性质，如自旋流和自旋扩散，以及各种响应和散射性质，这项工作应该为各种实验研究，包括输运，中子散射和核磁共振实验提供定量支持。这些研究应该有助于对这类材料的全面了解，并为它们可能用于下一代量子技术做好准备。除了它们对理解奇异量子材料和技术的科学价值外，这些研究还为本科生和研究生提供了理论和计算方法方面的极好培训基础。该奖项反映了NSF的法定使命，并通过使用基金会的智力优势和更广泛的影响审查标准进行评估，被认为值得支持。

项目成果

Divergence of magnetic susceptibility in the SU( N ) Nagaoka-Thouless ferromagnet

SU(N)Nagaoka-Thouless铁磁体的磁化率散度

• DOI: 10.1103/physrevb.106.014424
• 发表时间: 2022
• 期刊: Physical Review B
• 影响因子: 3.7
• 作者: Singh, Rajiv R.;Oitmaa, Jaan
• 通讯作者: Oitmaa, Jaan

Griffiths-McCoy singularities in the dilute transverse-field Ising model: A numerical linked cluster expansion study

稀横向场伊辛模型中的 Griffiths-McCoy 奇点：数值关联簇扩展研究

• DOI: 10.1103/physreve.99.032129
• 发表时间: 2019
• 期刊: Physical Review E
• 影响因子: 2.4
• 作者: Thompson, Foster;Singh, Rajiv R. P.
• 通讯作者: Singh, Rajiv R. P.

Magnetism of competing high-spin/low-spin states in Ba2NiO2(AgSe)2 and related two-orbital two-electron systems

• DOI: 10.1103/physrevb.105.064406
• 发表时间: 2021-08
• 期刊: Physical Review B
• 影响因子: 3.7
• 作者: Rajiv R. P. Singh

High-field expansion approach to kagome antiferromagnets with Dzyaloshinskii-Moriya interactions

• DOI: 10.1103/physrevb.100.121108
• 发表时间: 2019-05
• 期刊: Physical Review B
• 影响因子: 3.7
• 作者: Michael O. Flynn;Rajiv R. P. Singh

Rapid filling of the spin gap with temperature in the Schwinger-boson mean-field theory of the antiferromagnetic Heisenberg kagome model

• DOI: 10.1103/physrevb.99.155151
• 发表时间: 2018-07
• 期刊: Physical Review B
• 影响因子: 3.7
• 作者: Jad C. Halimeh;Rajiv R. P. Singh