Persistent currents through a quantum impurity: Protection through integrability

Abstract

We consider an integrable model of a one-dimensional mesoscopic ring, with the conduction electrons coupled by a spin exchange to a magnetic impurity. A symmetry analysis based on a Bethe ansatz solution of the model reveals that the current is insensitive to the presence of the impurity. We argue that this is true for any integrable impurity-electron interaction, independent of the choice of physical parameters or couplings. We propose a simple physical picture of how the persistent current gets protected by integrability.