Dresden 2017 – wissenschaftliches Programm

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HL: Fachverband Halbleiterphysik

HL 35: Focus Session: Topological Insulators on Coupled Quantum Wells (joined session with TT)

HL 35.4: Hauptvortrag

Dienstag, 21. März 2017, 10:30–11:00, POT 151

Progress in Edge Channel Transport of Two-Dimensional Topological Insulators — •Hartmut Buhmann — Physikalisches Institut, EP3, Universität Würzburg, Würzburg, Germany

The discovery of the quantum spin Hall (QSH) effect is already ten years old. However, an undisturbed edge channel transport has rarely been reported especially for samples which exceed a few micrometers in size, even though the QSH-states are protected against backscattering by time reversal symmetry. The reasons are manifold but mainly due to the fact that two-dimensional topological insulators are based on narrow gap semiconductors. Small disturbances and inhomogeneity may already result in potential fluctuations which introduce locally metallic electron or hole puddles. Edge channels traversing such puddles are no longer protected and backscattering destroys the expected perfect quantized conductance.

In this presentation I will review the experimental observations on two-dimensional topological insulators and give examples of how one can achieve almost perfect quantization in narrow gap samples. Taking special care during the fabrication process and taking advantage of charge accumulation at certain interfaces of the sample layer stack it becomes possible to observe quantized edge channel conductance even in sample exceeding the elastic mean free path. With these samples it is now possible to address various still open questions on the specific properties of the transport in helical edge channel as for example aspects of the magnetic field and temperature dependence.