Clemson University


Visualization of Topological States of Matter Using Microwave Impedance Microscopy


Dr. Monica Allen, Department of Physics, University of California, San Diego



Quantum-relativistic materials often host electronic phenomena with exotic spatial distributions.  In particular, topological insulators are characterized by metallic surface states that are topologically protected from backscattering by time-reversal symmetry, rendering the conductivity of the material robust against edge disorder. We employ microwave impedance microscopy (MIM), which characterizes the local complex conductivity of a material, to directly visualize chiral edge modes and phase transitions in a magnetic topological insulator. The key to our approach is the use of a novel cryogenic near-field imaging technique, which detects the unique fingerprint of topological edge modes in the GHz regime and disentangles them from trivial impurity states in the bulk of the material. Looking forward, we will also discuss the application of MIM more broadly to visualize edge currents in Chern insulators and present recent progress on the construction and testing of a new milliKelvin microwave impedance microscope.





Monica Allen is an Assistant Professor of Physics at UC San Diego.  She completed her B.A. and Ph.D. in Physics at Harvard University, where she used quantum transport measurements to investigate low-dimensional electronic phenomena in graphene.  After completing her PhD, Monica was a Karel Urbanek Postdoctoral Fellow in the Applied Physics Department at Stanford University, where she utilized high-frequency imaging techniques to visualize topological electronic states of matter.





Dial-In Information              Meeting code 462888

Thursday, April 14, 2022 at 4:00pm

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Lectures / Seminars / Speakers, Seminars

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Faculty, Alumni, Students, Undergraduate, Graduate, Postdocs


College of Science, Physics and Astronomy

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Kim Webb

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