Acoustoelectric current and pumping in a ballistic quantum point contact

The acoustoelectric current induced by a surface acoustic wave (SAW) in a b allistic quantum point contact is considered using a quantum approach. We f ind that the current is of the " pumping " type and is not related to drag, i.e., to the momentum transfer from the wave to the electron gas. At gate voltages corresponding to the plateaus of the quantized conductance the cur rent is small. It is peaked at the conductance step voltages. The peak curr ent oscillates and decays with increasing SAW wave number for short wavelen gths. These results contradict previous calculations, based on the classica l Boltzmann equation.