Local Moment and Heavy Fermion Physics

局域矩和重费米子物理

• 批准号: 1309929
• 负责人: Piers Coleman
• 金额: $ 27万
• 依托单位: Rutgers University New Brunswick
• 依托单位国家: 美国
• 项目类别: Continuing Grant
• 财政年份: 2013
• 资助国家: 美国
• 起止时间: 2013-09-01 至 2016-08-31
• 项目状态: 已结题
• 来源: https://www.nsf.gov/awardsearch/showAward?AWD_ID=1309929&HistoricalAwards=false
• 关键词: Local; Moment; Heavy; Fermion; Physics

TECHNICAL SUMMARYThis award supports theoretical research and education to study the correlated, collective behavior of electrons in heavy electron materials. These are lanthanide or actinide intermetallic compounds in which the close vicinity to magnetic instability gives rise to fundamentally new kinds of electronic material behavior. Motivated by many new experimental results, a theoretical study of the break-down of conventional metallic behavior that occurs in a quantum critical heavy fermion metal will be carried out. This will involve developing theoretical models for the "intrinsic" quantum criticality recently discovered in Ytterbium rare earth heavy fermion systems YbBAl3 and YbAuAl. Specifically, the research is aimed to develop a mixed boson-fermion theoretical framework to describe the co-existence of localized magnetism and delocalized heavy electron behavior that is observed to occur in various Cerium-based heavy electron materials.A second part of the research will study the development of novel forms of electronic order in heavy-electron materials. The PI will develop theoretical models for the 115 heavy fermion superconductors to understand the entanglement of the local moment spin degrees of freedom with the pair condensate, described by "composite pairing", and the unusual robustness of these superconductors against pair breaking. This research will also study the phenomenon of hidden order URu2Si2 and analogous praseodymium heavy electron materials. NON TECHNICAL SUMMARYThis award supports theoretical research and education to study the fundamental origins of new kinds of order in heavy fermion materials. Electrons in metals interact with one another via their mutual Coulomb repulsion. When these interactions become large, the conventional metallic state becomes unstable and the electrons organize themselves via a phase transition, into new states of order. Ordered states include familiar ferro-magnets in which the intrinsic magnetism of each of the electrons is aligned, anti-ferromagnets, in which the magnetic order is staggered in space, and superconductors in which electrons form of a fluid of Cooper pairs which flows without resistance. These new states bring new kinds of materials properties, such as the fierce magnetism used for hybrid car motors, or the zero resistance of a high temperature superconductor. Phase transitions that occur at the absolute zero of temperature are entirely driven by the zero-point quantum motion of the electrons; there is no thermal motion. Through quantum phase transitions, metals develop new forms of electronic order. In many quantum phase transitions, the transition to order is preceded by a point where the quantum mechanical jiggling of the emergent order becomes very intense, spreading throughout the entire metal. This kind of "Quantum Criticality" develops when the phase transition temperature is tuned to absolute zero. This award supports research to advance current understanding of the transformations in metallic behavior induced near a magnetic quantum critical point. The research will be focused on "heavy fermion" materials, whose properties make them highly tunable for the study of quantum criticality. The PI aims to develop a new mathematical framework to describe the transformation in the magnetic character of the electrons at a quantum critical point, as they transform from mobile waves to localized magnetic moments. A second part of this research concerns the new kinds of electronic order that develop in heavy fermion materials near a magnetic instability. The PI will focus in part on heavy fermion superconductors, which display in miniature, much of the physics observed in high temperature transition metal superconductors. Normal superconductivity develops in response to the formation of Cooper pairs between electrons. This research will refine the concept of "composite pairs", whereby magnetic moments bind to electron pairs to form a "composite pair" that drives superconductivity.The PI will also investigate the phenomenon of "hidden order" observed to develop as a precursor to superconductivity in the heavy fermion compound Uranium Ruthenium-2 Silicon-2 . The PI seeks to generalize the concepts that underlie a new kind of order he has proposed, called hastatic order, and to understand its relationship to the superconductivity that develops with the hidden order. The possibility that similar types of order can occur in closely related intermetallic materials will be examined.

技术摘要这一奖项支持理论研究和教育，以研究重型电子材料中电子相关的集体行为。这些是灯笼或acttinide的金属层间化合物，其中与磁不稳定性的近距离产生了从根本上产生新型的电子材料行为。 在许多新的实验结果的动机中，将进行一项对传统金属行为的分解的理论研究，该研究将在量子临界重型金属中进行。 这将涉及开发最近在ytterbium稀土沉重的费米式系统ybbal3和ybaual中发现的“内在”量子关键性的理论模型。具体而言，该研究的目的是开发混合的玻色子特性理论框架，以描述局部磁性和离域重型电子行为的共存，观察到在各种基于处值的重型电子材料中发生。研究的第二部分研究将研究重型电子材料中新型电子顺序的发展形式的发展。 PI将开发115个重型费米昂超导体的理论模型，以了解局部矩旋转自由度的纠缠与对配对凝结物的纠缠，并通过“复合配对”描述，以及这些超导体与成对破裂的异常鲁棒性。 这项研究还将研究隐藏顺序URU2SI2和类似praseodymuim重型电子材料的现象。非技术摘要这一奖项支持理论研究和教育，以研究重型费米昂材料中新秩序的基本起源。金属中的电子通过相互的库仑排斥相互作用。当这些相互作用变大时，常规金属状态就会变得不稳定，电子通过相变到新的秩序状态。有序状态包括熟悉的铁磁铁，其中每个电子的固有磁性是对齐的，抗铁磁铁的，其中磁性在太空中交错，而超导体则形成了库珀的流体的库珀对流体，这些流体不受阻力流动。 这些新状态带来了新型的材料特性，例如用于混合汽车电动机的猛烈磁性，或高温超导体的零电阻。 在温度的绝对零处发生的相变是完全由电子的零点量子运动驱动的。没有热运动。通过量子相变，金属开发了电子秩序的新形式。 在许多量子相变，向顺序的过渡之前是一个点，即紧急阶的量子机械跳动变得非常强烈，并散布在整个金属中。 当相变温度调谐到绝对零时，这种“量子关键性”会发展。该奖项支持研究，以提高对磁量子临界点附近金属行为转变的当前理解。这项研究将集中在“重型费米昂”材料上，其特性使其具有高度调整量量子临界。 PI旨在开发一个新的数学框架，以描述电子在量子临界点上从移动波转换为局部磁矩的磁性特征的转换。这项研究的第二部分涉及在磁不稳定性附近在重型费米昂材料中发展的新型电子顺序。 PI将部分集中在繁重的费米式超导体上，这些超导体显示在微型中，这些物理在高温过渡金属超导体中观察到的许多物理学。正常的超导性响应于电子之间的库珀对的形成。这项研究将完善“复合对”的概念，从而使磁矩与电子对结合，形成一个“复合对”，从而驱动超导性。PI还将研究观察到的“隐藏顺序”的现象，从而发展为在重型Fermion ruthenium ruthenium ruthenium-ruthenium-ruthenium-ruthenium-2硅2。 PI试图概括他提出的一种新秩序，称为Hastatic秩序的概念，并了解其与隐藏秩序发展的超导性的关系。将检查在密切相关的金属间材料中可能发生类似类型的秩序的可能性。