Edge and Bulk Transport in a Two-Dimensional Topological Insulator Based on a CdHgTe Quantum Well

The transport response of a CdHgTe quantum well with a thickness of 11.5 nm is investigated. The behavior of the local and nonlocal resistance in the temperature range from 0.1 to 20 K is examined. It is shown that the system under study is a two-dimensional topological insulator. In comparison with traditional two-dimensional topological insulators implemented in 8-nm-thick HgTe quantum wells, the investigated one is characterized by a significantly smaller energy gap and, at the same time, a higher carrier mobility. The data are analyzed using computer simulations taking into account the actual geometry of the sample, as well as scattering between edge and bulk carrier states. It is shown that the backscattering probability of topological electrons within the edge states is nearly independent of temperature. In contrast, the probability of scattering from the edge channels into the bulk depends exponentially on the temperature, and fitting this dependence with a standard activation formula is the most accurate way to determine the mobility gap in the system under study. Even at the highest temperature, the probability of scattering between the counter-propagating states of the same edge exceeds the probability of scattering into the bulk by an order of magnitude. Therefore, this mechanism is dominant and determines the mean free path of edge electrons.