SMEARING OF QUANTUM STATES AND GIANT OSCILLATIONS OF THE ACOUSTOELECTRIC CURRENT IN A QUANTUM CHANNEL

A quantum theory for the de current induced by a surface acoustic wave (the acoustoelectric current) in a uniform quasi-one-dimensional quan tum channel has been worked out. In long ballistic channels, giant osc illations of the acoustoelectric current were observed. According to t he theoretical predictions (Gurevich et al 1996 Phys. Rev. Lett. 77 38 81), in a perfect uniform channel a finite acoustoelectric current exi sts only if the acoustic frequency exceeds the specific threshold valu e which is determined by the momentum and energy conservation laws. Ho wever, a finite current has been clearly observed well below the thres hold. In the present paper, we show that electron scattering against a random short-range potential leads to an additional backscattering, a s well as to a smearing of the momentum conservation law. As a result, a finite current appears well below the threshold acoustic frequency. The analysis is performed using the Keldysh non-equilibrium Green's f unction technique.