Nonlocal resistance and its fluctuations in microstructures of band-inverted HgTe/(Hg,Cd)Te quantum wells

We investigate experimentally transport in gated microsctructures containing a band-inverted HgTe/Hg0.3Cd0.7Te quantum well. Measurements of nonlocal resistances using many contacts prove that in the depletion regime the current is carried by the edge channels, as expected for a two-dimensional topological insulator. However, high and nonquantized values of channel resistances show that the topological protection length (i.e., the distance on which the carriers in helical edge channels propagate without backscattering) is much shorter than the channel length, which is similar to 100 mu m. The weak temperature dependence of the resistance and the presence of temperature dependent reproducible quasiperiodic resistance fluctuations can be qualitatively explained by the presence of charge puddles in the well, to which the electrons from the edge channels are tunnel-coupled.