Title: Imaging current in two-dimensional topological insulators

Abstract:

The discovery of topological phases of matter has opened the door to an exciting array of phenomena with dissipationless electrical transport, non-abelian quasi-particles and even emergent supersymmetry being examples. To realize and control these anticipated phenomena we need to further improve the materials involved and integrate them with superconductors, ferromagnets as well as electrostatic gating. Magnetic imaging can contribute to this endeavour by locally probing current, magnetism and superconductivity. 

 

In this talk, I will give an overview of scanning superconducting quantum interference device (SQUID) microscopy as a versatile and non-invasive magnetic imaging technique. As an example, I will then showcase our measurements on HgTe quantum wells, the first experimentally demonstrated two-dimensional topological insulator (2D TI). Magnetic imaging allowed us to directly visualize that the current in devices made from this material is carried by the edges when tuned into the bulk energy gap - a key characteristic of a 2D TI. In addition, from the images we disentangled conduction through the edges and the interior of a device, allowing us to study the resistance of only the edges even when the interior becomes conductive through either gating or raising the temperature. If time permits, I will discuss strategies to improve the spatial resolution of our measurements to sub-micron length scales through a combination of improved image reconstruction and smaller sensor sizes and outline opportunities for magnetic imaging.