Nonlocal transport via edge states in InAs/GaSb coupled quantum wells

We have investigated low-temperature electronic transport on InAs/GaSb double quantum wells, a system which promises to be electrically tunable from a normal to a topological insulator. Hall bars of 50 mu m in length down to a few micrometers gradually develop a pronounced resistance plateau near charge neutrality, which comes along with distinct nonlocal transport along the edges. Plateau resistances are found to be above or below the quantized value expected for helical edge channels. We discuss these results based on the interplay between imperfect edges and residual local bulk conductivity.