Quantum Spin Liquids in Correlated f-Electron Compounds

摘要：在最低温度下，几乎所有的材料最终都会进入有序状态。在一维或二维的宇宙中，情况会大不相同，在那里奇异的量子自旋液态可能会出现。了解在这种状态下热量和电荷的传输方式才刚刚开始，而控制它来制造实用的设备和传感器已经成为一项核心挑战。该项目将识别和合成新材料，以寻找金属量子自旋液体。中子散射实验将在橡树岭国家实验室和国家标准与技术研究所的国家设施中进行。本科生和研究生都参与这些实验的各个方面，在测量技术和应用方面接受全面的培训和广泛的经验，这将使他们成为这些国家设施未来的有效用户。技术摘要：量子自旋液体（QSL）是在磁序被强量子涨落淹没时产生的，产生具有异常激发的大量纠缠基态，通常具有拓扑特征。虽然金属QSL预计具有更丰富的相位行为范围，但迄今为止发现的少数QSL系统都是绝缘的。在受挫时刻与流动传导电子耦合的本质金属量子层的发现，有可能实现和测试奇异态和相的理论预测，如非常规超导、铁磁性和激发具有光子样色散的狄拉克金属。这个项目试图在f电子基重费米子中找到第一个金属QSL的例子，并解释如何通过费米表面的坍塌来破坏传统的磁秩序或形成磁矩，这可能是金属中QSL形成的一般途径。实验程序是基于金属R2T2X （R=Ce,Yb）化合物，其中强量子涨落是由平面和链状形态的二聚化和磁序之间的竞争引起的。支持该实验计划所需的高质量单晶将在我们的实验室中从金属助熔剂中生长。中子衍射、磁强计、热容量和电输运测量将是解释潜在的磁性和电子相图的主要工具，辅以非弹性中子散射测量，将评估相应的磁波动和相关性的发展。该奖项反映了美国国家科学基金会的法定使命，并通过使用基金会的知识价值和更广泛的影响审查标准进行评估，被认为值得支持。

Nontechnical Abstract: Almost all materials will ultimately settle into an ordered state at the lowest temperatures. The situation would be much different in a universe that is one- or two dimensional, and where the exotic quantum spin liquid state may emerge. Understanding the ways in which the transport of heat and charge occurs in such a state is just beginning, and controlling it to create practical devices and sensors has emerged as a central challenge. This project will identify and synthesize new materials in search for a metallic quantum spin liquid. Neutron scattering experiments will be carried out at national facilities at Oak Ridge National Laboratory and at the National Institute of Standards and Technology. Both undergraduate and graduate students participate in all aspects of these experiments, receiving thorough training and broad experience in measurement techniques and applications that will prepare them to become effective future users of these national facilities. Technical Abstract: Quantum Spin Liquids (QSL) occur when magnetic order is overwhelmed by strong quantum fluctuations, giving rise to massively entangled ground states with unusual excitations, often with topological character. While metallic QSLs are expected to have a much richer range of phase behaviors, the few QSL systems discovered so far are all insulating. The discovery of intrinsically metallic QSLs where frustrated moments are coupled to itinerant conduction electrons has the potential to realize and to test theoretical predictions of exotic states and phases like unconventional superconductivity, ferromagnetism, and Dirac metals where excitations have photon-like dispersions. This project seeks to find the first examples of metallic QSLs among the f-electron based heavy fermions, and to explicate how the breakdown of conventional magnetic order or alternatively the formation of magnetic moments via the collapse of the Fermi surface can be generic routes to QSL formation in metals. The experimental program is based on the metallic R2T2X (R=Ce,Yb) compounds, where strong quantum fluctuations arise from competition between dimerization and magnetic order in both planar and chainlike morphologies. The high quality single crystals required to support this experimental program will be grown in our lab from metallic fluxes. Neutron diffraction, magnetometry, heat capacity, and electrical transport measurements will be primary tools for explicating the underlying magnetic and electronic phase diagrams, supplemented by inelastic neutron scattering measurements that will assess the corresponding development of magnetic fluctuations and correlations.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.