On the accuracy of conductance quantization in spin-Hall insulators
S. K. Konyzheva, E. S. Tikhonov, V. S. Khrapai
Institute of Solid State Physics, Russian Academy of Sciences, 142432 Chernogolovka, Russa
Moscow Institute of Physics and Technology, 141700 Dolgoprudny, Russia
Abstract
In contrast to the case of ordinary quantum Hall effect,
the resistance of ballistic helical edge channels in typical quantum spin-Hall
experiments is non-vanishing, additive and poorly quantized. Here we present a
simple argument connecting this qualitative difference with a spin relaxation in
the current/voltage leads in an experimentally relevant multi-terminal bar
geometry. Both the finite lead resistance and the spin relaxation contribute to
a non-vanishing four-terminal edge resistance, explaining poor quantization
quality. We show that corrections to the four-terminal and two-terminal
resistances in the limit of strong spin relaxation are opposite in sign, making
a measurement of the spin relaxation resistance feasible, and estimate the
magnitude of the effect in HgTe-based quantum wells.