CAREER: Correlated States in the Surface of Kondo Insulators

University Of California-Irvine, Irvine CA

Investigators

Abstract

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.