Charge pumping and current quantization in surface acoustic-wave-driven carbon nanotube devices

We investigate charge pumping in semiconducting carbon nanotubes by a travelling potential wave on the surface of a piezoelectric quartz substrate. We estimate the magnitude and profile of the potential wave as its passes the nanotubes and show how this results in the pumping of charge in packets. By tuning the potential of a side gate, transport of either electron or hole packets can be realized, reversing the direction of the current. We furthermore discuss a specific device in which the current shows a distinct plateau as a function of gate voltage, wave amplitude and frequency. Interestingly, the current plateau appears at a value of ef, where e is the electron charge and f the frequency of the potential wave. We discuss possible mechanisms that would lead to current quantization in our devices.