SFB Seminar

Since their first realization in conventional GaAs-based two-dimensional electron gases, quantum point contacts have become a basic building block of mesoscopic physics. Realizing such devices in the new material class of two-dimensional topological insulators would provide a powerful tool for transport experiments. Given the spatial proximity of the device edges, a quantum point contact in a quantum spin Hall system is expected to enable the investigation of helical tunnelling and interaction effects and is thus envisaged to enrich the understanding of helical edge states. Here, we present the lithographic fabrication of top gated quantum point contacts in HgTe quantum wells utilizing a novel multi-step wet etching technique. We examine the transport behaviour of a topological quantum point contact with the Dirac point located within the band gap and compare the acquired data with the conductance of a trivial structure. The gate voltage dependence of the conductance shows the expected quantization in integer steps of 2e^2/h as well as a value of G0 = 2e^2/h within the gap for the topological device. However, for thicker quantum wells, where the Dirac point is no longer located within the bulk gap, we observe the surprising emergence of an additional plateau at e^2/h in the conductance. Models for the origin of this plateau will be presented.