Single and multiparticle scattering in helical liquid with an impurity

We examine the scattering behavior from a single nonmagnetic impurity in a helical liquid. A helical liquid is a one-dimensional system with a pair of counterpropagating edge states, which are time reversal partners. In the absence of a magnetic field, time reversal symmetry is conserved and hence single-particle scattering is prohibited. However, multiparticle processes are possible. We examine the backscattering current and noise, and derive the effective scattering charge. A magnetic field enhances the backscattered current, but reduces the effective scattering charge. We find that the scattering charge can vary between e and 2e, depending on the strength of electron-electron interactions and the magnetic field.