CAREER: Correlated States in the Surface of Kondo Insulators

非技术摘要：高度有用、有时甚至是奇异的功能材料通常从电子彼此强烈相互作用的固体中出现。这些所谓的“强相关材料”的特性无法从单个电子的详细知识中直接推断出来，因此常常给我们带来惊喜：用于MRI诊断的高温超导体、iPod内的巨磁阻材料等等。该项目旨在探索和理解一类称为“近藤绝缘体”的相关材料表面的新型量子态。我们的研究团队已经发现了一种这样的材料 SmB6，它具有奇异的金属表面，该表面围绕着真正的绝缘体，并受到时间反转对称性的保护。这项职业资助允许在几个近藤绝缘体上进行晶体生长、测量和器件制造，以揭示表面状态的本质。通过扩展，它们不寻常的电子和热特性可用于容错量子计算、仿生信息处理和量子计量等技术应用。该项目整合了多个教育组成部分，包括课程开发、中学推广和学生科学培训。特别是，来自圣安娜贫困地区的高中志愿者以及加州大学欧文分校加州少数族裔参与联盟项目的本科生研究员的科学参与预计将激发他们的兴趣，并为他们从事科学技术职业做好准备。 技术摘要：这项职业补助金资助强相关近藤绝缘体表面状态的制造和实验研究。当前凝聚态物理学的一个焦点是了解电子相关性会给拓扑有序材料带来什么。近藤绝缘体，特别是 SmB6，是典型的强相关材料，具有 f 电子物理和一些非常不寻常的电子特性。最近，拓扑近藤绝缘体理论预测了其中一些材料中存在拓扑非平凡表面态。随后的实验，包括我们自己的实验，都证明了 SmB6 的金属表面状态及其与拓扑图的一致性。关于表面态的确切性质以及由于表面态内部以及表面与本体之间的相互作用而产生的不寻常特性，仍然存在疑问。该项目旨在回答其中一些问题，并使用近藤绝缘体作为平台，探索具有电子关联、重费米子物理和拓扑顺序的不寻常量子相。采用结合晶体生长、输运、光学、热和力测量的系统方法来揭示表面电子的动力学和能量学，了解表面的热特性，并通过化学掺杂、磁场、应变和压力研究可能的量子相变。该项目融入了几个重要的教育组成部分。这笔赠款用于开发研究生物理课程、实验室中学外展活动以及对处于职业生涯各个阶段的学生进行培训。即使没有先进的物理知识，来自圣安娜贫困地区的高中志愿者也可以部分学习和执行晶体生长。一些设备制造是由加州大学欧文分校加州少数族裔参与联盟项目的本科生研究人员在我们的集成纳米系统研究设施接受纳米制造培训后进行的。通过该项目，研究生将接受有关低温物理、晶体生长和高精度光学仪器的广泛而综合的培训，这将为他/她将来从事复杂的学术或行业工作做好准备。

Non-technical abstract: Highly useful and sometimes exotic functional materials often emerge from solids where electrons interact strongly with each other. The properties of these so-called "strongly correlated materials" cannot be directly inferred from the detailed knowledge of individual electrons, and therefore often give us pleasant surprises: high temperature superconductors for MRI diagnosis, giant magneto-resistance materials inside iPods, just to name a few. This project aims at exploring and understanding novel quantum states in the surface of a class of correlated materials called "Kondo insulators". One such material SmB6 has already been found, in part by our research team, to host an exotic metallic surface that surrounds the truly insulating bulk and is protected by time-reversal symmetry. This CAREER grant allows crystal growth, measurements and device fabrications on several Kondo insulators in order to unveil the nature of the surface state. By extension their unusual electronic and thermal properties can be exploited for technological applications such as fault-tolerant quantum computing, bio-inspired information processing and quantum metrology. Several educational components are integrated into this project, consisting of course developments, middle school outreach and scientific trainings for students. In particular, the scientific involvements by high school volunteers from disadvantaged regions in Santa Ana, as well as undergraduate researcher from UC Irvine's California Alliance for Minority Participation program are expected to generate interest and prepare them for careers in science and technology. Technical abstract: This CAREER grant funds the fabrication and experimental investigation of surface states in strongly correlated Kondo insulators. A current focus of condensed matter physics is to understand what electron correlation will bring to topologically ordered materials. Kondo insulators, in particular SmB6 are prototypical strongly correlated materials featuring f-electron physics and some quite unusual electronic properties. Recently the theory of topological Kondo insulator has predicted in some of these materials the existence of a topological nontrivial surface state. Subsequent experiments including our own have demonstrated in SmB6 the metallic surface state and its consistency with the topological picture. Questions remain about the exact nature of the surface state, and its unusual properties due to interactions within the surface state and between the surface and bulk. This project aims at answering some of these questions as well as using Kondo insulators as a platform for exploring unusual quantum phases with electron correlation, heavy Fermion physics and topological order. A systematic approach incorporating crystal growth, transport, optical, thermal and force measurements is used to unveil the kinetics and energetics of surface electrons, to understand the thermal properties of the surface, and to investigate the possible quantum phase transitions by chemical doping, magnetic field, strain and pressure. Integrated into this project are several important educational components. The grant allows the development of a graduate physics course, in-lab middle school outreach activities, and the training of students at various stages of their career. The crystal growth can be learnt and performed in part by high school volunteers from disadvantaged regions in Santa Ana even without advanced knowledge of physics. Some of the device fabrication is performed by undergraduate researches from California Alliance for Minority Participation program at UC Irvine, after receiving nano-fabrication trainings in our Integrated Nanosystems Research Facility. Through this project, a gradate student receives broad but integrated trainings on low temperature physics, crystal growth and high precision optical instrumentation, which will prepare him/her for sophisticated academic or industry jobs in the future.