Investigating quantum critical and topological dynamics in f-electron materials

摘要：基于镧系元素和锕系元素的材料包含了丰富的新特性，具有基础科学兴趣和潜在应用于当前和未来的技术。这些f电子量子材料在元素周期表中以镧和锕开始。在这里，我们寻找基于镧系元素和锕系元素的新量子材料。这具体包括含有铈、镨、钐、铕、镱和铀的材料。对物理性质和基础物理学的详细研究将以描述与技术相关的基本兴趣的惊人现象为主要目标。这些研究有望产生推动技术应用的新材料。这包括热电冷却和发电、磁热制冷、磁传感器、磁信息存储、量子计算、电子产品的高温超导、磁共振成像以及电能的产生、传输和存储。该项目有助于博士后学者、研究生和本科生的教育和培训，其中一些学生来自代表性不足的群体。PI及其小组成员参与社区外展活动，包括为高中生和本科生参观实验室，在当地小学进行科学演示，以及举办大众讲座。技术摘要：基于镧系元素和锕系元素的f电子量子材料包含丰富的相关电子相和现象库，包括价涨落、重费米子行为、近道绝缘子行为、量子临界性、非费米液体行为、金属-绝缘子跃迁、非常规超导性、磁性和电荷顺序以及拓扑现象。相互竞争的相互作用可以通过改变非热控制参数（如化学成分、压力和磁场）来“调谐”，从而导致包含大量这些相关电子相和现象的复杂相图。特别感兴趣的是非常规的超导性，奇异磁相和低温下的非费米液体行为，这些物理性质发生在量子临界点附近，其中二阶相变（通常是反铁磁）被抑制到0 K。拟议研究的目标是表征这些非凡的阶段和现象，确定它们形成的条件，确定潜在的微观机制，并测试适当的理论。该方法涉及材料合成（特别是单晶）和测量这些材料的输运、热和磁性能作为温度、成分和磁场的函数。这与使用超快光学光谱的准粒子动力学测量相补充，提供了一种强大的手段来询问和暂时解开电荷，自旋，晶格和轨道自由度。广泛的相关f电子材料，如填充的角方石化合物和近藤绝缘体硼化钐，一个候选的相关电子拓扑绝缘体，及其合金将被研究。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: Lanthanide- and actinide-based materials comprise a rich reservoir of new and novel properties of fundamental scientific interest and potential applications in current and future technologies. These f-electron quantum materials are found in the periodic table of the elements starting with lanthanum and actinium. Here we search for new quantum materials based on lanthanide and actinide elements. This specifically includes materials containing cerium, praseodymium, samarium, europium, ytterbium and uranium. Detailed investigations of the physical properties and underlying physics will be pursued with the primary goal of characterizing the striking phenomena of fundamental interest and relevance to technology. These studies are expected to yield new materials that will advance technological applications. This includes thermoelectric cooling and electrical power generation, magnetocaloric refrigeration, magnetic sensors, magnetic information storage, quantum computing, and high temperature superconductivity for electronics, magnetic resonance imaging, and the generation, transmission, and storage of electrical energy. This program contributes to the education and training of postdoctoral scholars and graduate and undergraduate students, some of which are from underrepresented groups. The PI's and their group members are involved in community outreach activities, including laboratory tours for high school and undergraduate students, science demonstrations at local elementary schools, and popular lectures.Technical Abstract: Lanthanide- and actinide-based f-electron quantum materials comprise a rich reservoir of correlated electron phases and phenomena, including valence fluctuations, heavy fermion behavior, Kondo insulator behavior, quantum criticality, non-Fermi liquid behavior, metal-insulator transitions, unconventional superconductivity, magnetic and charge order, and topological phenomena. Competing interactions can be "tuned" by varying non-thermal control parameters such as chemical composition, pressure, and magnetic field, leading to complex phase diagrams containing a multitude of these correlated electron phases and phenomena. Of particular interest are unconventional superconductivity, exotic magnetic phases and non-Fermi liquid behavior in low temperature physical properties that occur in the vicinity of a quantum critical point where a second order phase transition (usually, antiferromagnetic) is suppressed to 0 K. The objectives of the proposed research are to characterize these extraordinary phases and phenomena, determine the conditions under which they are formed, identify underlying microscopic mechanisms, and test appropriate theories. The approach involves materials synthesis (particularly single crystals) and measurement of the transport, thermal, and magnetic properties of these materials as a function of temperature, composition and magnetic field. This is complemented with quasiparticle dynamics measurements using ultrafast optical spectroscopy, providing a powerful means to interrogate and temporally disentangle charge, spin, lattice, and orbital degrees of freedom. A broad range of correlated f-electron materials such as filled skutterudite compounds and the Kondo insulator samarium boride, a candidate for a correlated electron topological insulator, and its alloys will be investigated.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.