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.

该奖项支持理论研究和教育，以研究重电子材料中电子的相关集体行为。这些是镧系或锕系金属间化合物，其中与磁不稳定性密切相关的是从根本上产生新的电子材料行为。 受许多新的实验结果的启发，将对量子临界重费米子金属中发生的传统金属行为的崩溃进行理论研究。 这将涉及开发理论模型的“内在”量子临界最近发现的镱稀土重费米子系统YbBAl 3和YbAuAl。具体而言，本研究旨在建立一个混合玻色子-费米子理论框架，以描述在各种铈基重电子材料中观察到的局域磁性和离域重电子行为的共存。第二部分研究重电子材料中新的电子有序形式的发展。PI将为115个重费米子超导体开发理论模型，以了解局域矩自旋自由度与对凝聚体的纠缠，由“复合配对”描述，以及这些超导体对对破坏的不寻常的鲁棒性。 本研究还将研究URu_2Si_2和类似的镨系重电子材料的隐序现象。该奖项支持理论研究和教育，以研究重费米子材料中新秩序的基本起源。金属中的电子通过它们的相互库仑排斥相互作用。当这些相互作用变大时，传统的金属状态变得不稳定，电子通过相变组织自己，进入新的有序状态。有序态包括熟悉的铁磁体，其中每个电子的固有磁性是对齐的;反铁磁体，其中磁序在空间上交错;以及超导体，其中电子形成库珀对的流体，其流动没有阻力。 这些新的状态带来了新的材料特性，例如用于混合动力汽车发动机的强烈磁性，或者高温超导体的零电阻。 在绝对零度下发生的相变完全是由电子的零点量子运动驱动的;没有热运动。通过量子相变，金属形成了新的电子秩序形式。 在许多量子相变中，有序的转变之前有一个点，在这个点上，涌现的有序的量子力学抖动变得非常强烈，遍布整个金属。 这种“量子临界性”在相变温度被调整到绝对零度时发展。该奖项支持研究，以促进当前对磁量子临界点附近诱导的金属行为转变的理解。这项研究将集中在“重费米子”材料上，这些材料的特性使它们在量子临界研究中具有高度可调性。 PI的目标是开发一个新的数学框架来描述在量子临界点的电子的磁特性的转变，因为它们从移动的波转变为局部磁矩。这项研究的第二部分关注的是在磁不稳定性附近的重费米子材料中发展出的新型电子秩序。 PI将部分集中在重费米子超导体上，这些超导体以微型显示，在高温过渡金属超导体中观察到的大部分物理学。正常的超导性是由于电子之间形成库珀对而产生的。该研究将完善“复合对”的概念，即磁矩与电子对结合形成驱动超导性的“复合对”。PI还将研究在重费米子化合物铀钌-2硅-2中观察到的作为超导性前兆发展的“隐藏秩序”现象。PI试图概括他提出的一种新秩序（称为hastatic秩序）的概念，并理解它与随着隐藏秩序发展的超导性的关系。类似类型的顺序可能发生在密切相关的金属间化合物材料的可能性将被检查。