Frustration and Order in Heavy Fermions on the Shastry-Sutherland Lattice

*技术摘要*本奖项旨在阐明最初定位在稀土基重费米子化合物的f轨道上的电子可以被诱导加入组成费米面(FS)的巡游态的过程，以及伴随这种电子解禁转变的电子结构的临界波动。在几何受挫的Shastry-Sutherland晶格上形成的重费米子中，受挫在抑制磁序中的作用将被研究。设想了两个不同的基态：自旋液体和费米液体，其中传导电子从波动矩中解耦，因此其电子被排除在FS之外，而费米液体中强烈的近藤效应使f电子离域，而f电子现在被并入扩展的FS中。在T=0时，这两个无序态是由大小FS态之间的涨落驱动的纯电子跃迁而分开的。合成新材料以支持PI和她的合作者的测量计划是该项目的中心主题。参与的本科生和研究生将在各种不同的合成和实验技术方面获得实用和可移植的经验。这项研究广泛使用了国家研究设施，包括NIST和橡树岭国家实验室的中子散射中心。*非技术摘要*尽管所有材料在高温下都是无序的，它们的构型没有明显的模式或相关性，但随着温度的降低，超导或磁性等有序相的开始是压倒性的。这个项目试图解释具有最极端有序形式的系统的性质，这种形式恰好发生在绝对零度的温度下。这种相变的量子力学性质至关重要，其结果是，即使在非零温度下，热或电的传导等正常行为也会发生重大改变。在这里，将使用与磁矩晶格相关的几何约束来实现这种T=0转变，并将使用NIST和橡树岭国家实验室进行的中子散射实验来研究它们的性质。合成新材料以支持PI和她的合作者的测量计划是该项目的中心主题。参与的本科生和研究生将在各种不同的合成和实验技术方面获得实用和可移植的经验。

****Technical Abstract****This award aims to explicate the process by which electrons that are initially localized on the f-orbitals of rare earth based heavy fermion compounds can be induced to join the itinerant states comprising the Fermi surface(FS), and the critical fluctuations of the electronic structure that accompany this electronic de-confinement transition. The role of frustration in suppressing magnetic order in heavy fermions that form on the geometrically frustrated Shastry-Sutherland lattice will be investigated. Two distinct ground states are envisaged: a spin liquid where the conduction electrons are decoupled from the fluctuating moments, whose electrons are consequently excluded from the FS, and a Fermi liquid, where a strong Kondo effect delocalizes the f-electrons, which are now incorporated in an expanded FS. These two non-ordered states are separated at T=0 by a purely electronic transition, driven by fluctuations between the large and small FS states. The synthesis of new materials to support both the measurement program of the PI and those of her collaborators is a central theme of this project. Participating undergraduate and graduate students will gain practical and portable experience in a variety of different synthesis and experimental techniques. This research makes extensive use of national research facilities, including neutron scattering centers at NIST and Oak Ridge National Laboratory. ****Non-Technical Abstract****While all materials are disordered at high temperatures, with no discernible patterns or correlations in their configurations, the onset of an ordered phase such as superconductivity or magnetism is overwhelmingly favored as the temperature is reduced. This project seeks to explicate the properties of systems with the most extreme form of order, which occurs exactly at a temperature of absolute zero. The quantum mechanical nature of such a phase transition is paramount, with the result that normal behaviors like the conduction of heat or electricity are drastically modified- even at nonzero temperatures. Here, geometrical constraints associate with a lattice of magnetic moments will be used to realize such T=0 transitions, and their properties will be studied using neutron scattering experiments carried out at NIST and at Oak Ridge National Laboratory. The synthesis of new materials to support both the measurement program of the PI and those of her collaborators is a central theme of this project. Participating undergraduate and graduate students will gain practical and portable experience in a variety of different synthesis and experimental techniques.