CAREER: Backscattering, Confinement and Superconductivity in a Two-Dimensional Topological Insulator

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Non-Technical: The smaller and smaller scales of conventional computer circuits are rapidly approaching dimensions at which quantum mechanical phenomena become unavoidable. At these scales it will be paramount to understand how to harness these quantum effects in order to build more powerful computers. Recently, a new class of materials with unique properties has been discovered, which could play an important role for future information processing technologies. These "topological insulators" are electrically insulating in the bulk, but can conduct charge along their boundaries. This CAREER project studies the electronic properties of InAs/GaSb, a two-dimensional topological insulator (2D TI), a material in which electrons flow through edge channels. This project will first shed light on the effects of impurities on the electrical resistance of these edge channels and determine the role of magnetic interactions on charge flow. Furthermore, recent theoretical work has predicted that a 2D TI placed in contact with a superconductor (a metal which conducts charge without energy losses) can host Majorana states. These novel quantum mechanical states could have a transformative impact on fault-tolerant quantum computing. A second objective of this project is therefore to realize and detect Majorana states in a 2D TI-superconductor device. Beyond training graduate and undergraduate students for future careers in science and the high-technology industry, the principal investigator (PI) will promote broader interest in quantum physics, nanoscience and their applications through activities at local science museums and social media. A central educational goal is to increase the Native-American student participation in physics and STEM by launching an internship in the PI's lab and helping to organize a series of annual week-long summer camps for Native-American high-school students and their teachers at the University of Minnesota. Technical: This project studies backscattering, confinement, topological superconductivity, and Majorana states in InAs/GaSb double quantum wells, a two-dimensional topological insulator (2D TI). Understanding backscattering and confinement of 2D TI helical edge modes is a significant open problem in condensed matter physics, and is important for applications that would harness spin-polarized ballistic transport. The research team uses induced quantum dots to simulate charge and spin impurities, which have been theorized to affect backscattering. Nanoscale magnetic insulator barriers are investigated as a means of confining the edge modes using magnetic exchange coupling. 2D TIs are also ideal systems for realizing topological superconductivity and for observing and manipulating Majorana zero-energy modes. Majorana modes have been predicted to exhibit non-Abelian, anyonic exchange statistics, and could play a key role for the development of decoherence-protected topological quantum bits. One of the main objectives of this project is therefore to realize and detect topological superconductivity and Majorana modes. To this end, the research team will investigate hybrid devices made by contacting InAs/GaSb with conventional superconductors. The research project is closely integrated with an extensive educational plan to train graduate and undergraduate students for successful careers in science and the high-technology industry and help educate the broader public about nanoscience. A central goal is to increase Native-American student participation in physics and STEM disciplines.