Nonadiabatic quantum pumping in mesoscopic nanostructures

We consider a nonadiabatic quantum pumping phenomenon in a ballistic narrow constriction. The pumping is induced by a potential that has both spatial and temporal periodicity characterized by K and Omega. In the zero frequenc y (Omega = 0) limit, the transmission through narrow constriction exhibits valley structures due to the opening up of energy gaps in the pumping regio n - a consequence of the K periodicity. These valley structures remain robu st in the regime of finite Omega, while their energies of occurrence are sh ifted by about h Omega /2. The direction of these energy shifts depend on t he directions of both the phase-velocity of the pumping potential and the t ransmitting electrons. This frequency dependent feature of the valley struc tures gives rise to both the asymmetry in the transmission coefficients and tho pumping current. An experimental setup is suggested for a possible obs ervation of our nonadiabatic quantum pumping finding. (C) 2001 Published by Elsevier Science Ltd.