Thermoelectric figure of merit in topological insulators

Transport behavior of two-dimensional topological insulators is theoretically studied in narrow ribbon geometry. The system has perfectly conducting edge channels, which are free from backscattering. At high temperature, the bulk states dominate in the transport phenomenon. However, at low temperature the conducting channels along the edges become dominant. It causes a bulk-to-edge crossover. Namely, by lowering temperature, the figure of merit first decreases by a competition between the bulk and the edge transport, and then increases again because the edge transport become larger.