Dynamic response of a double barrier system: The effect of contacts

We study the dynamical response of a double-barrier conductor with two contacts to investigate the contact effect on ac conduction in the system. We have presented the calculation of various physical quantities such as the distributions of internal potential and charge density, capacitance and low-frequency ac conductance. We show that the characteristic potentials would tend to unity (zero) in the reservoirs. When the system is far away from resonance, the charge distribution exists only around the barrier regions as a response to the applied voltage, and hence the contacts almost have no effect on the results. In the case of small transmission probability, we find a considerable amount of charge distribution surrounding the double-barrier conductor. As for the resonant case or near the resonance, our results show that the charge distribution displays large fluctuations outside the conductor, but almost no charge distribution within the conductor. In this case, the effect of contacts on the charge and potential distributions is considerable. Moreover, we find that qualitatively the presence of contacts does not change the main features of the emittance without contacts. But the contact effect on the capacitance is significant when the chemical potential is very close to resonant energy: there is a sharp capacitance peak at resonance that does not exist in the case without contacts.