CAREER: Correlated Topological Phases in Rare-earth-based Compounds

摘要：根据载体的运动特性，材料可分为两类：金属和绝缘体。金属导电是因为电子的自由运动，而绝缘体不能导电。拓扑绝缘体（TI）是一种新的物质状态，在这种状态下，材料在其整体上是不导电的，但保证其表面具有非常稳定的导电状态。这种表面传导受到材料底层对称性基本约束的保护，不受干扰。材料的拓扑性质是当代凝聚态物理学中一个引人入胜的研究课题。第一个TI的发现极大地加速了对以非平凡拓扑状态为特征的物质相的研究，如狄拉克，Weyl和节线半金属，拓扑晶体绝缘体和拓扑超导体。狄拉克和Weyl半金属提供了一个研究体态（线性色散）和表面态（费米弧）的平台。值得注意的是，迄今为止，通过实验实现的大多数观察到的拓扑材料都是在弱相关电子能带系统中发现的，其中电子之间的相关性在很大程度上被忽略了。本研究旨在发现和理解拓扑材料中的电子相关性。拓扑量子材料有望在自旋电子学和量子计算等下一代技术领域开创一个新时代。这些领域的进步有助于提高以更高速度存储和处理大量数据的能力。还有其他具有战略意义的应用，如密码学和安全通信。该项目旨在通过美国物理学会（APS）资助的桥梁项目，帮助招募、指导和培养代表性不足的少数民族学生进入物理学博士课程，并通过“physstec”项目增加高素质高中物理教师的培养。根据量子材料的进展编写教育材料，以帮助学生，教师和公众。技术摘要：自2007年发现第一个三维拓扑绝缘体材料以来，拓扑材料领域呈指数级增长。它目前正在影响世界范围内凝聚态物理、化学、材料科学和工程社区的大型机构。此外，到目前为止，大多数工作都集中在简单材料上，其中电子相关效应可以在很大程度上被忽略，并且拓扑性质可以用单粒子带结构很好地描述。强电子相关的引入为拓扑绝缘状态的研究开辟了一个新的领域。该项目旨在发现和理解强相关电子系统中不寻常的狄拉克费米子态，这些新态的相关性性质与石墨烯，拓扑绝缘体和Weyl半金属中的相关性明显不同。具体来说，本项目利用高分辨率角分辨、自旋分辨和时间分辨光谱学技术来研究稀土（4f）基化合物的电子和自旋特性以及体的动量分辨动力学特性和对称保护表面特性，以发现和理解强相关拓扑相的可能特征。计划的研究提供了相关拓扑相、重Weyl费米子相和磁性拓扑绝缘体相及其光-物质相互作用的电子签名，从而为强相关性促进的拓扑相和Weyl相的研究开辟了新的方向。该项目的教育部分是激励从高中到大学的学生从事量子材料的研究，使他们成为凝聚态物理、光谱学、真空技术、激光技术和纳米科学领域的潜在领导者。教育计划创造了一个激励、教育并为年轻一代提供必要机会的系统，让他们采取行动，成为未来的科学家。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。

Non-Technical Abstract: Materials can be classified into two categories based on the movement of the carriers: metals and insulators. Metals conduct electricity because of the free movement of the electrons whereas insulators cannot conduct electricity. The topological insulator (TI) is a new state of matter in which a material is non-conducting throughout its bulk but is guaranteed to have very stable conducting states on its surface. This surface conduction is protected against disturbance by the basic constraints of the material's underlying symmetry. Topological properties of materials are a fascinating subject of study in contemporary condensed matter physics. The discovery of the first TI tremendously accelerated research into phases of matter characterized by non-trivial topological states such as Dirac, Weyl and nodal-line semimetals, the topological crystalline insulator, and the topological superconductor. Dirac and Weyl semimetals provide a platform to study both bulk (linearly dispersive) and surface (Fermi arc) states. It is important to note that, to date, most of the observed topological materials realized experimentally are found in weakly correlated electronic band systems where the correlation between the electrons are largely ignored. This research proposes to discover and understand the electron correlation in topological materials. Topological quantum materials promise to bring upon a new age in areas such as spintronics and quantum computation among other next generation technologies. Progress in these areas helps to increase the ability to store and process larger amounts of data at higher speeds. There are other applications of strategic interest such as cryptography and safe communications. This project aims to help recruit, mentor, and prepare underrepresented minority students into Physics PhD programs through the American Physical Society (APS)-funded Bridge Program as well as to increase the production of highly qualified high school Physics teachers through "PhysTEC" program. Education materials based on the progress of the quantum materials are prepared to help students, teachers and the general public.Technical Abstract: The field of topological materials has grown exponentially since the first three-dimensional topological insulator material was discovered in 2007. It is currently impacting large bodies of condensed matter physics, chemistry, materials sciences, and engineering communities worldwide. Moreover, most work thus far has focused on simple materials where electronic correlation effects can be largely ignored, and the topological properties are well described in terms of a single-particle band structure. The introduction of strong electron correlation opens up a novel field of research in a topological insulating state. This project aims to discover and understand the unusual Dirac fermion states in strongly correlated electron systems, the nature of the correlations in these novel states are distinctly different from those found in graphene, topological insulators, and Weyl semimetal. Specifically, this project utilizes high-resolution angle-, spin- and time-resolved photoemission spectroscopy techniques to study the electronic and spin properties as well as the momentum resolved dynamical properties of the bulk and symmetry-protected surface properties of rare-earth (4f)-based compounds to discover and understand the possible signature of the strongly correlated topological phase. The planned research provides the electronic signatures for the correlated topological phase, heavy Weyl fermion phase and magnetic topological insulator phases, as well as their light-matter interactions, thus opening up a new direction of research into the topological and Weyl phases facilitated by strong correlations. The educational component of the project is to motivate students from high schools to universities to pursue quantum materials research so that they become potential leaders in the field of condensed matter physics, spectroscopy, vacuum technology, laser technology and nanoscience. The educational plans create a system that inspires, educates, and provides the opportunities necessary for the younger generations to take steps and become the scientists of tomorrow.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.