Study of Disorder and the Emergence of a Robust Insulating Behaviour in Topological Kondo Insulator, Samarium Hexaboride

Regents Of The University Of Michigan - Ann Arbor, Ann Arbor MI

Investigators

Abstract

Nontechnical Abstract: Nature has provided a fascinating insulating material with many unique properties, mainly that it is the only electrical insulator whose properties do not vary much with increasing impurities or disorder. Research on this material, called samarium hexaboride, is important not only because of its unique properties but that it is at the intersection of two scientific fields ‐ correlated electron systems and topological materials. Understanding why this material has robust insulating behavior is the main goal of the project. Achieving this understanding will lead to new kinds of transport phenomena, such as unique one‐dimensional conduction through dislocations that should not be possible and which are difficult to observe in other topological materials. Novel transport methods will be developed in this work to explore this unique material that can be broadly used by other groups studying many other materials. Furthermore, this strange insulator, samarium hexaboride, is also an ideal material for studying the emergent properties of topologically protected surface electrons. This is important because this can pave the way for testing new and innovative spintronic and superconductor‐topological insulator hybrid devices. The educational component of this project provides excellent training for graduate and undergraduate students. The principal investigator will participate in outreach activities that are designed to excite K‐12 students about STEM fields. A unique, comprehensive physics study manual intended for all physics graduate students is being developed to help students to transition into graduate research. Technical Abstract: The robustness of insulating behavior against disorder, which was recently discovered using inverted resistance measurements, makes samarium hexaboride one of the most unique topological materials to study. This project investigates bulk and surface conduction in samarium hexaboride and its dilute alloys using inverted resistance, Hall, and Corbino measurements. To study surface conduction, an alternative transport analysis is employed to eliminate contributions to transport from subsurface cracks. One of the main objectives is to understand the gap formation and the underlying reasons for the robustness of bulk transport. To quantify the effects of disorder in this material, the research team is performing transport experiments on La‐, Fe‐, La‐, Ga‐, and Eu‐doped samples within a dilute doping range from 0.1 to 5%. In addition to point defects, this project looks at extended defects, including one‐dimensional dislocations, which can form conducting channels in topological insulators. If successful, the experimental realization of transport through a single one‐dimensional dislocation would allow the investigation of a new kind of topologically protected conduction mode. 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.