Regensburg 2016 – wissenschaftliches Programm

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TT: Fachverband Tiefe Temperaturen

TT 73: Low-Dimensional Systems: Topological Order

TT 73.7: Hauptvortrag

Donnerstag, 10. März 2016, 16:45–17:15, H19

Imaging currents in 2D quantum materials — •Katja Nowack — Cornell University, Ithaca, United States

Magnetic imaging is uniquely suited to the non-invasive imaging of current densities, particularly in 2D devices. In this talk, I will showcase this approach by discussing our measurements on HgTe quantum well devices in the quantum spin Hall (QSH) regime. In a nutshell, we scan a superconducting quantum interference device (SQUID) to obtain maps of the magnetic field produced by the current flowing in a device. From the magnetic image we reconstruct a 2D current distribution with a spatial resolution of several microns. This allowed us to directly visualize that the edges of the devices carry most of the current when tuned into their insulating gaps - a key feature of the QSH state. In addition, from the images we disentangle 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 both 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 interesting opportunities for current imaging.