Acoustoelectric effect in a finite-length ballistic quantum channel

The de current induced by a coherent surface acoustic wave (SAW) of wave ve ctor q in a ballistic channel of length L is calculated. The current contai ns two contributions, even and odd in q. The even current exists only in a asymmetric channel, when the electron reflection coefficients r(1) and r(2) , at both channel ends, are different. The direction of the even current do es not depend on the direction of the SAW propagation, but is reversed upon interchanging r(1) and r(2). The direction of the odd current is correlate d with the direction of the SAW propagation, but is insensitive to the inte rchange of r(1) and r(2). It is shown that both contributions to the curren t are nonzero only when the electron reflection coefficients at the channel ends are energy dependent. The current exhibits geometric oscillations as a function of qL. These oscillations are the hallmark of the coherence of t he SAW and are completely washed out when the current is induced by a flux of noncoherent phonons. The results are compared with those obtained previo usly by different methods and under different assumptions.