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.

技术总结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。这些是镧系元素或金属间化合物，其中靠近磁性不稳定的地方导致了从根本上新类型的电子材料行为。在许多新的实验结果的推动下，将对量子临界重费米子金属中发生的常规金属行为的分解进行理论研究。这将涉及为最近在YbBAl3和YbAuAl系统中发现的Yb稀土重费米子系统中发现的“本征”量子临界性建立理论模型。具体地说，这项研究旨在建立一个混合玻色子-费米子理论框架来描述在各种基于Ce3+的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。研究的第二部分将研究重电子材料中新的电子有序形式的发展。PI将为115个重费米子超导体建立理论模型，以了解局域力矩自旋自由度与双凝聚的纠缠，以及这些超导体对断裂的异常健壮性。这项研究还将研究隐藏有序URU2Si2和类似的Pr重电子材料的现象。非技术总结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。金属中的电子通过相互的库仑斥力相互作用。当这些相互作用变大时，传统的金属状态变得不稳定，电子通过相变组织起来，进入新的有序状态。有序状态包括常见的铁磁体，其中每个电子的本征磁性是对齐的；反铁磁体，其中的磁序在空间中交错；以及超导体，其中电子形成无阻力流动的库珀对流体。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电机的强烈磁性，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，在向有序的转变之前，出现的有序的量子力学抖动变得非常强烈，扩散到整个金属。当相变温度调到绝对零度时，就会产生这种“量子临界性”。该奖项支持推动当前对磁量子临界点附近金属行为转变的理解的研究。这项研究将集中在“重费米子”材料上，这种材料的性质使它们在量子临界性研究中具有高度的可调性。PI旨在开发一种新的数学框架来描述量子临界点上电子的磁性转换，因为它们从移动波转换为局域磁矩。这项研究的第二部分涉及在磁不稳定性附近的重费米子材料中发展的新类型的电子有序。PI将在一定程度上关注重费米子超导体，这种超导体展示了高温过渡金属超导体中观察到的大部分物理现象。正常的超导电性是由于电子之间形成库珀对而发展起来的。这项研究将完善“复合对”的概念，即磁矩与电子对结合形成一个“复合对”，以驱动超导。PI还将研究在重费米子化合物铀Ru-2-Silicon-2中观察到的作为超导先驱的“隐藏有序”现象。PI试图推广他提出的一种新秩序的基本概念，称为停顿秩序，并理解它与随着隐藏秩序发展而发展的超导电性的关系。将审查在密切相关的金属间材料中可能出现类似类型的有序的可能性。