Ultrasensitive Magneto-optic Imaging of Correlated Phases in Topological Materials

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Nontechnical Abstract: Future quantum computers and quantum devices will likely be based on materials that are protected from noise by their intrinsic features, making the operation of these devices robust against environmental perturbations. The fundamental physical nature of these complex materials and their phases, however, is just starting to be revealed. The research team focuses on two such phases: the chiral edge states found in the junction between a superconductor and a magnetic topological insulator, and on the surface of a slightly magnetized topological Kondo insulator, both holding promise for constructing robust quantum computers. In this project, the PI and his team use a set of experimental tools including precision magneto-optic imaging to investigate these two chiral edge states. The results could provide a knowledge base for topologically protected information processing, potentially operating at room temperature. The science and education components provide integrated and rigorous scientific training for graduate and undergraduate students, so including students from underrepresented groups. Through an outreach program, the excitement of science could be conveyed to minority and female middle school students. Technical Abstract: Chiral edge states are intricate topological structures that are potentially useful for quantum devices. However, much of their physics remains unknown. In this project, the PI and the research team utilize a newly developed mK-Sagnac interferometer-microscope in their group to image and investigate two such topological structures: the quantum anomalous Hall (QAH) state and the related Majorana chiral modes in a superconductor/QAH junction, and the magnetic chiral edge states on the surface of the topological Kondo insulator SmB6. As surface and bulk often have distinctively different physics properties in topological materials, in this project, the research team performs simultaneous Sagnac, torque magnetometry, and transport measurements to clearly distinguish the contributions from bulk and surface states down to unprecedented low temperatures. These measurements could resolve the intricate spin and magnetization structures on the edge and bulk states of QAH states, chiral Majorana edge mode, and SmB6 surface magnetic structure. This project can potentially address important questions in the field of topological materials and devices: 1. Can we stabilize QAH effect at temperatures close to ambient temperature for practical device applications? 2. What are the spin structures of the chiral Majorana edge mode? 3. What is the nature of the quantized conductance found in the surface state of topological Kondo insulator? The science and education components provide integrated and rigorous scientific training for graduate and undergraduate students, so including students from underrepresented groups. Through an outreach program, the excitement of science could be conveyed to minority and female middle school students.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.