Role of displacement current in quantum-dot turnstile devices

The dynamics of the current and the electron number in quantum-dot turnstile devices, in which the heights of the tunneling barriers are modulated by external rf signals, is studied theoretically within the adiabatic approximation. The displacement current is more accurately quantized than the tunneling currents flowing through both the left and the right barriers, since the leakage current is compensated. We find numerically that an electron tunnels through the barrier before its height reaches the minimum value. The tunneling phases of rf signals, at which an electron can actually tunnel, change as the amplitude of rf signals and the barrier height and width are varied. We also discuss the conditions for the current quantization. The dc I-V curve which we obtain shows a plateau at each quantized current nef with width e2/C + AE and sharp steps between neighboring plateaus. Whenever the dc current is quantized, the change of the number of electrons in the quantum dot during one half-period of rf signal is an integer.