CAREER: Monopole Superconductivity and Ferromagnetism of Itinerant Electrons

职业：单极超导和流动电子的铁磁性

• 批准号: 1848349
• 负责人: Yi Li
• 金额: $ 53.79万
• 依托单位: Johns Hopkins University
• 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 2024-06-30
• 项目状态: 已结题
• 来源: https://www.nsf.gov/awardsearch/showAward?AWD_ID=1848349&HistoricalAwards=false
• 关键词: CAREER; Monopole; Superconductivity; Ferromagnetism; Itinerant

NONTECHNICAL SUMMARYThis CAREER award supports theoretical research and education in unusual states and fundamental questions that arise in the study of metallic materials. A piece of metal contains many electrons that are moving and interacting with each other. Quantum mechanics governs their collective behavior, which can give rise to new states of matter manifesting as electron order. Consider an example of order from our everyday classical world, a team of swimmers can control and change their position as a whole by performing a synchronized change in the shapes their bodies assume. An analogous phenomenon in quantum systems is called many-body Berry phases: due to quantum mechanical effects, electrons in a material can synchronize and exhibit collective effects. The electrons can be induced to organize in many different ordered states, some of which have not been observed before. This project advances fundamental concepts by exploring the mathematical description of order as well as its physical consequences. The project can potentially lead to developing a new platform for quantum computation.The PI will also tackle the long-standing problem of uncovering the microscopic mechanism behind the magnetism some metals exhibit. This is a formidable problem because of the failure of a common theoretical assumption, namely that electrons moving in a crystal of atoms can be considered independently. In fact, the motion of any one electron is strongly correlated with the motion of all others. The PI and her research team will combine analytic and numerical methods to tackle this challenge. Apart from theoretical insight, the project could lead to technological applications that harness these strong correlation phenomena.This award will enable a range of educational and outreach activities, from mentoring graduate, undergraduate, and high-school students, to developing new course materials aligned with the research project that cover the application of modern mathematical approaches in condensed matter physics. The PI will also initiate an interactive community outreach program targeting Pre-K and K-12 students and their parents, aimed at enhancing the public's interest in and appreciation of quantum physics and the research frontier.TECHNICAL SUMMARYThis CAREER award supports theoretical research and education in new quantum phenomena of itinerant electrons arising from the interplay of topology, interaction, and strong correlation. Specifically, the PI will focus on developing a theory framework for new classes of many-body topological states, and on a nonperturbative approach to itinerant ferromagnetism in strongly correlated multiorbital systems. The PI and her group will investigate novel classes of three-dimensional topological many-body ordering states characterized by monopole harmonic symmetries, including both superconducting and density-wave states. The particle-particle (Cooper) pairing, or, particle-hole pairing, inherits nontrivial Berry phases from Fermi surface topology. Their gap functions cannot be globally well-defined in momentum space, and thus go beyond the standard realization of rotational symmetry based on spherical harmonics. Consequently, they exhibit topologically protected nodal structures regardless of specific ordering mechanism and can only be characterized by monopole harmonic functions.Itinerant ferromagnetism is the ferromagnetism of mobile electrons based on Fermi surface instabilities rather than the ordering of local spin moments. However, it lacks a well-controlled weak-coupling description; a precise answer to the relation between orbital degeneracy and the mechanism of ferromagnetism has so far been lacking, mostly due to the lack of nonperturbative results for handling strong magnetic fluctuations. The PI and her group will develop nonperturbative methods, combining analytic approaches and unbiased numerical simulations, to study the role of orbital degeneracy in the mechanism of itinerant ferromagnetism and strong correlation effects of itinerant electrons close to ferromagnetic transitions.This award will enable a range of educational and outreach activities, from mentoring graduate, undergraduate, and high-school students, to developing new course materials aligned with the research project that cover the application of modern mathematical approaches in condensed matter physics. The PI will also initiate an interactive community outreach program targeting Pre-K and K-12 students and their parents, aimed at enhancing the public's interest in and appreciation of quantum physics and the research frontier.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.

非技术摘要这一职业奖支持在金属材料研究中出现的异常状态和基本问题的理论研究和教育。一块金属包含许多正在移动和相互作用的电子。量子力学控制着它们的集体行为，这可以引起新的物质状态作​​为电子秩序。考虑一下我们日常古典世界的秩序示例，一组游泳者可以通过对身体的形状进行同步变化来控制和改变整个位置。量子系统中的类似现象称为多体浆果阶段：由于量子机械效应，材料中的电子可以同步并表现出集体效应。可以诱导电子在许多不同的有序状态中组织，其中一些以前没有观察到。该项目通过探索顺序的数学描述及其物理后果来推进基本概念。该项目可能会导致开发一个新的量子计算平台。PI还将解决一些长期存在的问题，即某些金属展示的磁性背后的微观机制。这是一个巨大的问题，因为常见理论假设的失败，即可以独立考虑在原子晶体中移动的电子。实际上，任何一个电子的运动都与所有其他电子的运动密切相关。 PI和她的研究团队将结合分析和数值方法来应对这一挑战。除了理论洞察力外，该项目还可能导致技术应用，以利用这些强大的相关现象。该奖项将使从指导毕业生，本科生和高中生到开发与一致的新课程材料相结合的一系列教育和外展活动涵盖现代数学方法在冷凝物理物理学中的应用的研究项目。 PI还将启动针对Pre-K和K-12学生及其父母的互动社区外展计划，旨在增强公众对量子物理学和研究边界的兴趣和欣赏。由拓扑，相互作用和强相关性的相互作用引起的巡回电子的新量子现象。具体而言，PI将着重于为新的多体拓扑状态类别开发理论框架，并致力于在密切相关的多用途系统中的巡回铁磁学的非扰动方法。 PI和她的小组将研究以单极谐波对称性（包括超导和密度波状态）为特征的三维拓扑多体有序状态的新型类别。粒子粒子（库珀）配对或粒子孔配对，从费米表面拓扑结构继承了非平凡的浆果相。它们的间隙函数在动量空间中不能在全球范围内定义明确，因此超出了基于球形谐波的旋转对称性的标准实现。因此，它们表现出拓扑保护的淋巴结结构，而不论特定的有序机制，只能以单极和谐功能为特征。Itinerant的铁磁性是基于费米表面不稳定性的移动电子的铁磁性，而不是局部旋转时刻的顺序。但是，它缺乏控制良好的弱耦合描述。到目前为止，缺乏对轨道退化和铁磁学机制之间关系的确切答案，这主要是由于缺乏处理强磁波动的非扰动结果。 PI和她的小组将开发非扰动方法，结合分析方法和公正的数值模拟，以研究轨道退化性在流动的铁磁性机制中的作用，而迄今为止的巡回电子效果与临近铁磁过渡的差异范围。从指导毕业生，本科生和高中生到开发与研究项目一致的新课程材料，该项目涵盖现代数学方法在凝结物理学中的应用。 PI还将启动针对Pre-K和K-12学生及其父母的互动社区外展计划，旨在增强公众对量子物理和研究边界的兴趣和欣赏。该奖项反映了NSF的法定任务，并被视为被视为值得通过基金会的智力优点和更广泛的影响审查标准来通过评估来支持。

项目成果

Ferromagnetic percolation transition in a multiorbital flat band assisted by Hund's coupling

洪德耦合辅助下多轨道平带中的铁磁渗流跃迁

• DOI: 10.1103/physrevb.104.064442
• 发表时间: 2021
• 期刊: Physical Review B
• 影响因子: 3.7
• 作者: Bobrow, Eric;Zhang, Junjia;Li, Yi
• 通讯作者: Li, Yi

Monopole charge density wave states in Weyl semimetals

• DOI: 10.1103/physrevresearch.2.012078
• 发表时间: 2018-10
• 期刊: Physical Review Research
• 影响因子: 4.2
• 作者: Eric Bobrow;Canon Sun;Y. Li