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

非技术摘要：根据载体的运动，材料可以分为两类：金属和绝缘体。金属导电是因为电子能自由移动，而绝缘体不能导电。拓扑绝缘体（TI）是一种新的物质状态，其中材料在其整个体积中是不导电的，但保证在其表面上具有非常稳定的导电状态。这种表面传导受到材料潜在对称性的基本约束的保护，不受干扰。材料的拓扑性质是当代凝聚态物理学中一个非常有趣的研究课题。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，外尔和半金属，拓扑晶体绝缘体和拓扑超导体。狄拉克和外尔半金属提供了一个平台，研究体（线性色散）和表面（费米弧）状态。值得注意的是，到目前为止，大多数观察到的实验实现的拓扑材料都是在弱相关的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关联。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带来一个新时代。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）资助的桥梁计划帮助招募，指导和准备代表性不足的少数民族学生进入物理博士课程，并通过“PhysTEC”计划增加高素质高中物理教师的产量。技术摘要：自2007年第一个三维拓扑绝缘体材料被发现以来，拓扑材料领域的发展呈指数级增长。它目前正在影响全球凝聚态物理，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的材料中，电子相关效应可以在很大程度上被忽略，并且拓扑性质可以很好地描述为单粒子能带结构。强电子关联的引入为拓扑绝缘态的研究开辟了一个新的领域。该项目旨在发现和理解强关联电子系统中不寻常的狄拉克费米子态，这些新态中的关联性质与石墨烯，拓扑绝缘体和Weyl半金属中发现的那些明显不同。具体而言，该项目利用高分辨率角分辨、自旋分辨和时间分辨光电子能谱技术研究稀土（4f）基化合物的电子和自旋性质以及体相和非晶保护表面性质的动量分辨动力学性质，以发现和理解强相关拓扑相的可能特征。计划中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的电子签名，以及它们与轻物质的相互作用，从而开辟了强相关促进的拓扑和Weyl相研究的新方向。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研究，使他们成为凝聚态物理学、光谱学、真空技术、激光技术和纳米科学领域的潜在领导者。该教育计划创建了一个系统，激励，教育，并提供必要的机会，让年轻一代采取步骤，成为明天的科学家。这个奖项反映了NSF的法定使命，并已被认为是值得通过评估使用基金会的智力价值和更广泛的影响审查标准的支持。

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.