CAREER: Electrical and Thermoelectric Transport Beyond the Metal/Insulator Paradigm

电子材料传统上分为两大类：金属和绝缘体。在这种二分法中，金属是可以通过电子的“费米表面”导电的材料，而绝缘体是不导电的材料，也没有这样的费米表面。但在过去的十年里，人们发现了一种全新的材料类别——“拓扑材料”，它挑战了既定的二分法。拓扑材料能够导电，但没有电子的费米表面。新技术和新物理现象的可能性在这种性质的组合中仍有待探索。该奖项支持研究、推广和教育的综合计划。研究活动的目的是在理论上探索拓扑材料中新的块状现象的可能性。研究的重点是热电特性（热到电的转换）和从导电到非导电状态转变的性质。关键问题包括：1)哪些条件和哪些材料有利于实现热到电的有效转换？2)金属到绝缘体转变的新形式是可能的，它们的实验特征是什么？新的拓扑热电材料在废热回收和更有效的冷却方面都有应用。了解金属-绝缘体过渡的新形式可能会导致新一代的电子设备。外展和教育活动为提高凝聚态物理作为一个领域的可见度和可及性，以及扩大参与做出了具体的步骤。活动包括(i)制定课程计划，向服务不足社区的小学生介绍电力和电气材料，（ii）为参加奥林匹克级别物理竞赛的高中生社区制定问题集和讲座，（iii）建立一个包容性的研究小组，并开发研究生和本科生级别的新课程。（iv）通过俄亥俄州立大学的“桥梁项目”（Bridge Program）指导来自代表性不足群体的学生；(v)开发向公众介绍凝聚态物理学的社交媒体内容。技术摘要：该奖项支持基于电子材料输运特性的综合研究、推广和教育计划。这项研究主要集中在拓扑材料上，与传统金属和绝缘体相比，拓扑材料有可能产生全新的输运性质和电子相。探索这些可能性需要超越导致拓扑材料发现和分类的非相互作用、自由粒子描述的理论。这项研究的目的是产生这样的理论，特别关注体热电输运和金属-绝缘体转变的性质。研究的一个重点是拓扑半金属的热电响应及其对磁场的依赖。PI和他的研究团队将考虑磁性Weyl半金属，补偿拓扑半金属和其他狄拉克/Weyl以外的拓扑材料。这项工作的目标是确定有利于实现大热电功率和大热电效率的条件和材料特性。第二个推力考虑拓扑系统如何承认新的大块金属绝缘体过渡，超越了典型的安德森和莫特的观点。研究小组将考虑这种转变的不同情况，包括在强无序系统，流体动力学系统和具有非微扰电子-声子耦合的电子系统中。这些工作的目标是揭示可能的新的电子量子现象，这些现象在导电性中有很强的表现，并说明它们如何在实际材料中出现。与这些研究工作相结合的是一项全面的推广和教育计划，该计划将采取具体步骤，提高凝聚态物理学作为一个领域的可见度和可及性，并扩大其参与范围。活动包括(i)制定课程计划，向服务不足社区的小学生介绍电力和电气材料，（ii）为参加奥林匹克级别物理竞赛的高中生社区制定问题集和讲座，（iii）建立包容性小组并开发研究生和本科生级别的新课程。（iv）通过俄亥俄州立大学（Ohio State University）的“桥梁项目”（Bridge Program），指导来自代表性不足群体的学生；(v)开发向公众介绍凝聚态物理学的社交媒体内容。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 AbstractElectronic materials are traditionally dichotomized into two broad classes: metals and insulators. In this dichotomy, metals are materials that can conduct electricity via a "Fermi surface" of electrons, and insulators are materials that do not conduct electricity and have no such Fermi surface. But the last decade has uncovered whole new classes of materials, "topological materials," that defy the established dichotomy. Topological materials are able to conduct electricity but have no Fermi surface of electrons. The possibilities for new technology and new physical phenomena inherent in this combination of properties remain largely to be explored.This award supports an integrated plan of research, outreach, and education. The research activities aim to explore, theoretically, the possibilities for new bulk phenomena in topological materials. The research focuses in particular on thermoelectric properties (the conversion of heat to electric power) and on the nature of the transition from conducting to non-conducting states. Key questions include these: 1) which conditions and which materials are conducive to achieving an efficient conversion of heat to electric power?, and 2) what new forms of the metal-to-insulator transition are possible, and what are their experimental signatures?New topological thermoelectric materials may have applications in both waste-heat recovery and more efficient cooling. Understanding new forms of the metal-insulator transition could lead to new generations of electronic devices.The outreach and education activities make concrete steps toward improving the visibility and accessibility of condensed matter physics as a field, and toward broadening participation within it. Activities include (i) developing lesson plans that introduce electricity and electric materials to elementary school students in underserved communities, (ii) developing problem sets and lectures for the community of high school students participating in olympiad-level physics competitions, (iii) building an inclusive research group and developing new courses at the graduate and undergraduate level, (iv) mentoring students from underrepresented demographic groups through the Bridge Program at Ohio State University, and (v) developing social media content that introduces condensed matter physics to the public.Technical AbstractThis award supports an integrated plan of research, outreach, and education that is based on the transport properties of electronic materials. The research focuses primarily on topological materials, which harbor the possibility for fundamentally new kinds of transport properties and electronic phases compared to those possible in traditional metals and insulators. Exploring these possibilities requires theories that go beyond the non-interacting, free-particle descriptions that led to the discovery and classification of topological materials. The aim of this research is to produce such theories, focusing in particular on bulk thermoelectric transport and on the nature of the metal-insulator transition.One thrust of the research is concerned with the thermoelectric response of topological semimetals and its dependence on magnetic field. The PI and his research team will consider magnetic Weyl semimetals, compensated topological semimetals, and other topological materials beyond Dirac/Weyl. The goal of this work is to identify conditions and material properties that are conducive to achieving large thermopower and large thermoelectric efficiency. A second thrust considers how topological systems admit novel bulk metal-insulator transitions, beyond the canonical Anderson and Mott perspectives. The research team will consider different scenarios for such transitions, including in strongly disordered systems, hydrodynamic systems, and in electron systems with nonperturbative electron-phonon coupling. The goal of these works is to uncover possible new electronic quantum phenomena, which have strong manifestations in the electrical conductivity, and to illustrate how they may appear in real materials.Integrated with these research efforts is a comprehensive plan for outreach and education that will take concrete steps toward improving the visibility and accessibility of condensed-matter physics as a field, and toward broadening participation within it. Activities include (i) developing lesson plans that introduce electricity and electric materials to elementary school students in underserved communities, (ii) developing problem sets and lectures for the community of high-school students participating in olympiad-level physics competitions, (iii) building an inclusive group and developing new courses at the graduate and undergraduate level, (iv) mentoring students from underrepresented demographic groups through the Bridge Program at Ohio State University, and (v) developing social media content that introduces condensed-matter physics to the public.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.