NONLINEAR RESPONSE AND ELECTRON-ELECTRON INTERACTIONS IN MESOSCOPIC METAL RINGS

A time-dependent electric field gives rise to a stationary non-equilib rium current I((2)) around a mesoscopic metal ring threaded by a magne tic flux. We show that this current, which is proportional to the inte nsity of the field, is closely related to the exchange part of the int eraction contribution to the equilibrium persistent current, and that the corresponding non-linear conductivity directly measures the weak l ocalization correction to the polarization. We explicitly calculate th e disorder average of I((2)) in the diffusive regime as function of th e frequency of the electric field and the static flux piercing the rin g, and suggest an experiment to test our theory.