Kondo interaction of quantum spin Hall edge channels with charge puddles

Since the first observation of the quantum spin Hall effect, it is known that the helical edge channel conductance exhibits fluctuations around the quantized value, in contrast to the (integer) quantum Hall effect. Here, the authors show, in a mechanistic study, that these fluctuations originate from spin-flip scattering mediated by charge puddles via a Kondo-type interaction, an effect which is expected to occur in any narrow-gap quantum spin Hall insulator.