Mesoscopic Charge Relaxation in a Strongly-Correlated Quantum Dot System

In this talk we present non-perturbative studies on the coherent ac
response of quantum dot-reservoir systems in the presence of strong
many-body correlations. The Coulomb repulsion and the spin exchange
coupling in the quantum dot are found to break the universality in the
charge relaxation resistance which was previously derived under the
general single-particle picture. We found that the charge relaxation
resistance has peaks at the relevant Kondo temperature and that the
zero-frequency resistance is considerably enhanced when the Zeeman
splitting is comparable to the Kondo temperature. Since the Kondo effect
depends highly on the spin correlations existing in the dot, diverse
features are also observed near the singlet-triplet transition. We
explain the observed enhancement of the relaxation resistance in terms
of the generation of particle-hole excitations in the reservoir
accomplished by spin-flip processes in the dot and discuss the relation
between the resistance and the spin fluctuations.