DYNAMIC PERSISTENT CURRENTS IN MESOSCOPIC RINGS

A dynamic current I-omega in a mesoscopic ring subjected to a time-dependent external magnetic field H(t) approximately = H0 + H-omega-cos(omega-t) is calculated in the limit of small H-omega using linear-response theory and the supersymmetry method. It is shown that the current I-omega remains finite in the limit omega --> 0 and exceeds currents obtained from thermodynamic considerations. It can be of the order of eD0/L2 for magnetic fluxes-phi approximately phi-0, where D0 is the classical diffusion coefficient, L is the circumference, and phi-0 = hc/e is the flux quantum, and has a component which oscillates in flux with the period phi-0/2. The derived current can explain the experiment by Levy et al.