Charge and spin dynamics of an interacting quantum dot

The subject of this talk is the relaxation behavior of a quantum dot, brought out of equilibrium by a time-dependent modulation, e.g. by a gate potential. We study a single-level quantum dot with strong Coulomb interaction, weakly coupled to a single lead, taking the role of a mesoscopic capacitor. The transient response to a fast change, as well as the stationary ac-response to a slow harmonic variation of the gate potential are computed by means of a real-time diagrammatic expansion in the tunnel-coupling strength. We compare the response in the charge of the dot to a step potential with the $RC$ time extracted from the ac response and find differences due to cotunneling contributions. This is in contrast to a classical capacitor, where these timescales are equal. Furthermore, we find that after a fast switching, the exponential relaxation behavior of charge and spin are governed by a single time constant each, which differ from each other due to Coulomb repulsion. A further relaxation rate is related to electron-hole correlations and can be extracted from deviations from the equilibrium charge.

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