Visualization of Topological States of Matter Using Microwave Impedance Microscopy

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 impervious to 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 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, van der Waals heterostructures, and Majorana modes in topological superconductors.