"Challenges to the textbook picture in 2D-topological insulator materials investigated by novel local probes"
Who: M. Reyes-Calvo, Nanoimaging Group nanoGUNE / Stanford University
Place: nanoGUNE seminar room, Tolosa Hiribidea 76, Donostia - San Sebastian
Date: Monday, 23 February 2015, 11:00
In the Quantum Spin Hall textbook picture, a 2-dimensional topologically non-trivial insulator (2d-TI) is expected to present conductive edge states protected against backscattering. The application of a magnetic field should lift this protection, and above a critical field the material would enter a trivial insulator regime, where the edge conduction fully disappears.
In real 2d-TI materials, such as inverted HgTe quantum wells, however, the picture seems to be more complex and scattering happens over long enough distances (around microns). Furthermore, although the resistance of the devices increases in the presence of a magnetic field, but some predictions, such as the removal of the edge conduction have not been yet directly probed.
In our work, we use novel local probe techniques to shed some light into the above challenges. On the one hand, Scanning Gate Microscopy results allow us to identify the microscopic origin of scattering in the quantum spin hall edge states. On the other hand, Microwave Impedance Microscopy results reveal that edge conduction persists unexpectedly at high magnetic fields. Finally, we propose the use of lateral heterojunctions to probe the nature of such unexpected states.