Quantum Spin Liquids in Correlated f-Electron Compounds

非技术摘要：几乎所有的材料最终都会在最低温度下进入有序状态。在一维或二维的宇宙中，情况会大不相同，在那里可能出现奇异的量子自旋液态。了解这种状态下热量和电荷的传输方式才刚刚开始，控制它以创建实用的设备和传感器已经成为一个核心挑战。 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加这些实验的各个方面，接受全面的培训和广泛的测量技术和应用经验，使他们能够成为这些国家设施的未来有效用户。 技术摘要：量子自旋液体（QSL）发生在磁序被强烈的量子涨落淹没时，产生具有不寻常激发的大规模纠缠基态，通常具有拓扑特征。虽然金属QSL被认为具有更丰富的相行为，但迄今为止发现的少数QSL系统都是绝缘的。本征金属QSL的发现，其中挫折时刻耦合到巡回传导电子有可能实现和测试的理论预测的异国情调的国家和阶段，如非常规超导，铁磁性，狄拉克金属的激发有光子一样的色散。该项目旨在寻找基于f-电子的重费米子中金属QSL的第一个例子，并解释如何通过费米表面的坍塌破坏常规磁序或形成磁矩可以成为金属中QSL形成的一般途径。实验方案是基于金属R2 T2 X（R=Ce，Yb）的化合物，其中强烈的量子波动产生的二聚和磁秩序在平面和链状形态之间的竞争。支持这个实验计划所需的高质量单晶将在我们的实验室中从金属熔剂中生长出来。中子衍射、磁力测量、热容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，该奖项反映了NSF的法定使命，并被认为是值得通过使用基金会的智力价值和更广泛的评估来支持。影响审查标准。

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.