Effect of many-body correlations on mesoscopic charge relaxation

We investigate nonperturbatively the charge relaxation resistance and quantum capacitance in a coherent RC circuit in the strong-coupling regime. We find that the many-body correlations break the universality in the charge relaxation resistance: (i) The charge relaxation resistance has peaks at finite frequencies Γ*/ℏ, where Γ* is an effective level broadening, and (ii) the zero-frequency resistance deviates from the universal value when the Zeeman splitting is comparable to Γ*. This behavior becomes even more prominent in the Kondo regime. The observed features are ascribed to the generation of particle-hole excitations in the contacts accomplished by spin-flip processes in the dot.