Nanoscale Magnetism and Unconventional Quantum Phases and Transitions

纳米级磁性和非常规量子相和跃迁

• 批准号: 0457440
• 负责人: Leon Balents
• 金额: $ 30万
• 依托单位: University of California-Santa Barbara
• 依托单位国家: 美国
• 项目类别: Continuing Grant
• 财政年份: 2005
• 资助国家: 美国
• 起止时间: 2005-07-15 至 2009-06-30
• 项目状态: 已结题
• 来源: https://www.nsf.gov/awardsearch/showAward?AWD_ID=0457440&HistoricalAwards=false
• 关键词: Nanoscale; Magnetism; Unconventional; Quantum; Phases

This grant involves two broad research projects in theoretical condensed matter physics: modeling and control of spin transport in nanostructures, and unconventional collective states of quantum matter in strongly correlated materials. Both areas are very active experimentally, and present important puzzles and challenges to existing theory.The spintronics project has several specific goals. A proper hydrodynamic theory of spin transport will be developed, with microscopic derivations of transport coefficients. Specific problems are to determine the structure of spin-charge coupling terms, their dependence upon various scattering processes, and experimental means of measuring these effects. Another project is spin relaxation in ferromagnetic diluted magnetic semiconductor materials, and how this enters the appropriate hydrodynamics. Finally, the non-hydrodynamic regime of single quantum spins will be considered,including their coherence effects and relaxation mechanisms. This research benefits from, and complements, existing experimental expertise in spintronics at UCSB.The project on unconventional phases and transitions is motivated by the realization in recent work that simple reasonable models can exhibit phases and quantum critical points completely outside the usual paradigms. Thus this project is aimed both at applying the emerging new conceptual framework to recent and long-standing puzzles in experimentally interesting materials, and, to a lessor extent, at extending and systematizing the framework itself. Some of the experimental phenomena to be studied are Mott charge ordering transitions, charge and spin frustration in spinels and rare earth intermetallics and their connection to heavy fermion behavior, and spin liquid states in organic and inorganic triangular lattice magnets. These problems will be addressed by a variety of analytical (field theory, renormalization group, gauge theory, bosonization) and numerical (exact diagonalization, variation wavefunction) techniques. The PI is familiar with a wide variety of such approaches, and has made substantial contributions in these fields prior to this grant.Intellectual Merit: These projects represent two different frontiers of condensed matter physics. Control and measurement of spin is undergoing an experimental revolution in techniques (e.g. time-resolved optical pump-probe spectroscopy, strain engineering of spin-orbit interactions, etc.) and materials (diluted magnetic semiconductors, digital magnetic structures). New mechanisms of collective quantum order and emergent behavior are reinvigorating the theoretical investigation of old outstanding problems - and suggesting new ones - in strongly correlated materials. Both fields are thus ripe for bringing new theoretical ideas into application, and thereby advancing the fundamental knowledge base of condensed matter physics.Broader Impacts: First and foremost, this work is designed to motivate and explain experiments and properties of materials. Moreover, the hydrodynamic models to be developed in the spintronics portion of the proposal in fact describe macroscopic transport phenomena: they are the spin analogs of Ohm's law for charge conduction. Detailed models of this type are clearly crucial for any applications. Educationally, graduate students and postdocs will be trained in these forefront areas of condensed matter theory, and new course materials will be developed to communicate theexcitement of the fields to new students. A comprehensive web site with colloquial and graduate student level explanations of the research will be developed to further communicate to a broader audience.

这项资助涉及理论凝聚态物理的两个广泛的研究项目：纳米结构中自旋输运的建模和控制，以及强相关材料中量子物质的非常规集体状态。这两个领域的实验都非常活跃，对现有理论提出了重要的难题和挑战。自旋电子学项目有几个具体的目标。一个适当的流体动力学理论的自旋输运将发展，与输运系数的微观推导。具体问题是确定自旋-电荷耦合项的结构，它们对各种散射过程的依赖，以及测量这些效应的实验方法。另一个项目是铁磁稀释磁性半导体材料中的自旋弛豫，以及它如何进入适当的流体动力学。最后，讨论了单量子自旋的非流体力学状态，包括它们的相干效应和弛豫机制。这项研究得益于并补充了UCSB现有的自旋电子学实验专业知识。非常规相和跃迁项目的动机是最近的工作认识到，简单的合理模型可以完全在常规范式之外展示相和量子临界点。因此，该项目旨在将新兴的新概念框架应用于实验中有趣的材料中最近和长期存在的难题，并且在较小程度上扩展和系统化框架本身。需要研究的实验现象包括：尖晶石和稀土金属间化合物中的Mott电荷有序跃迁、电荷和自旋受挫及其与重费米子行为的关系、有机和无机三角晶格磁体中的自旋液态。这些问题将通过各种解析（场论、重整化群、规范理论、玻色子化）和数值（精确对角化、变分波函数）技术来解决。PI熟悉各种各样的此类方法，并且在此之前在这些领域做出了重大贡献。学术价值：这些项目代表了凝聚态物理的两个不同前沿。自旋的控制和测量在技术（如时间分辨光泵浦探测光谱，自旋-轨道相互作用的应变工程等）和材料（稀释磁性半导体，数字磁性结构）方面正在经历一场实验革命。集体量子秩序和涌现行为的新机制在强相关材料中重新激活了对旧的突出问题的理论研究，并提出了新的问题。因此，这两个领域已经成熟，可以将新的理论思想引入应用，从而推进凝聚态物理的基础知识基础。更广泛的影响：首先，这项工作旨在激发和解释材料的实验和特性。此外，在提案的自旋电子学部分中发展的流体动力学模型实际上描述了宏观输运现象：它们是电荷传导的欧姆定律的自旋类似物。这种类型的详细模型显然对任何应用程序都至关重要。在教育方面，研究生和博士后将在这些凝聚态理论的前沿领域进行培训，新的课程材料将被开发出来，以向新生传达这些领域的兴奋。我们将建立一个综合的网站，以口语和研究生水平的研究解释，进一步与更广泛的受众交流。