Charging Effects in Ultrasmall Quantum Dots in the Presence of Time-Varying Fields

The influence of charging effects on time-dependent transport in small semiconductor quantum dots with arbitrary level spectra is studied. Starting from an explicit time-dependent tunneling Hamiltonian, a non-Markovian Master equation is derived which is also valid in the nonlinear response regime. The many-body nonequilibrium distribution functions of the dot are calculated and the I-V characteristic of the structure including the displacement currents is obtained. New resonant features show up in the Coulomb oscillations and in the Coulomb staircase, and a new possibility to realize electronic pumps is described.