Toroidal Scattering and Nonreciprocal Transport by Magnetic Impurities

We propose the second-order response of metals in an electric field induced by magnetic impurities which locally break inversion symmetry. The impurities with toroidal moments scatter conduction electrons in the presence of the spin-orbit coupling, leading to nonreciprocal response. This mechanism is ubiquitous when a magnetic impurity is placed off an inversion center such as an interstitial site and a surface of a two-dimensional system.