Condensed Matter Seminar - "Understanding Electronic Transport across Quantum Anomalous Hall Insulators and Superconducting Devices through Local Magnetic Measurements"

Electric charge can flow in unexpected ways through a sample, particularly in topological materials, superconducting devices, and non-uniform conductors. In this talk, I will discuss how we use a local magnetic probe to visualize electronic transport in different types of samples.

First, we visualize how a non-equilibrium current flows in a quantum anomalous Hall insulator by imaging the magnetic field produced by the current. Against the prevalent expectation that transport is concentrated along the edges, we find that current can flow through the interior of the sample while the Hall resistance remains quantized.

By exploiting the temperature dependence of the sample’s magnetization, we additionally image current-induced heating, revealing localized hot spots at the contacts at which the current enters the device.

We observe how the current-induced heating spreads throughout the device and ultimately drives breakdown of the quantized state. Second, I turn to superconducting devices, where proximity effects at interfaces between superconductors and normal metals shape electronic transport by modifying the superconducting transition.

Using spatially resolved imaging, we probe the structure of proximity effects in transition-edge sensors (TESs), which exhibit a rich interplay between superconductors, normal metals, and distinct superconductors.

We find that long-range proximity effects extend across the device, strongly shaping the superconducting transition and, in turn, device performance.