Elastic backscattering of quantum spin Hall edge modes from Coulomb interactions with nonmagnetic impurities

We demonstrate that electrostatic interactions between helical electrons at the edge of a quantum spin Hall insulator and dynamical impurity can induce quasi-elastic backscattering. Modelling as two-level system, we show transitions counterpropagating Kramers-degenerate electronic states occur without breaking time-reversal symmetry, provided also undergoes transition. The associated electrical resistance has weak temperature dependence down to non-universal scale. Our results extend range known backscattering mechanisms in modes include scenarios where electron tunnelling out system is absent.