Admittance of the SU(2) and SU(4) Anderson quantum RC circuits

We study the Anderson model as a description of the quantum RC circuit for spin-1/2 electrons and a single level connected to a single lead. Our analysis relies on the Fermi liquid nature of the ground state, which fixes the form of the low-energy effective model. The constants of this effective model are extracted from a numerical solution of the Bethe ansatz equations for the Anderson model. They allow us to compute the charge relaxation resistance R _q in different parameter regimes. In the Kondo region, the peak in R_q as a function of the magnetic field is recovered and proven to be in quantitative agreement with previous numerical renormalization group results. In the valence-fluctuation region, the peak in R_q is shown to persist, with a maximum value of h/2e2, and an analytical expression is obtained using perturbation theory. We extend our analysis to the SU(4) Anderson model where we also derive the existence of a giant peak in the charge relaxation resistance.