Helical edge transport in the presence of a magnetic impurity: The role of local anisotropy
The helical edge modes of 2D topological insulators are supposed to be protected from time-reversal invariant elastic backscattering. Yet substantial deviations from perfect conductance are typically observed experimentally down to very low temperatures. To resolve this conundrum we consider the effect of single magnetic impurity with arbitrary spin, taking into account for the first time the most general structure of their exchange interaction with the edge modes, as well as their local anisotropy. We find that the latter affects strongly the backscattering current in a wide range of voltages and temperatures. We demonstrate that the sensitivity of the backscattering current to the presence of local anisotropy is different for half-integer and integer values of the impurity spin. In the latter case the local anisotropy can significantly increase the backscattering correction to the current.