Quantized acoustoelectric current in a finite-length ballistic quantum channel: The noise spectrum

Fluctuations in the acoustoelectric current, induced by a surface acoustic wave propagating along a ballistic quantum channel, are considered. We focus on the large-wave-amplitude case, in which it has been experimentally found that the current is quantized, and analyze the noise spectrum. A phenomenological description of the process, in terms of a random pulse sequence, is proposed. The important ingredients of this description are the probabilities p(n) for a surface acoustic wave well to capture it electrons. It is found that from the noise characteristics one can obtain these probabilities, and also estimate the typical length scales of the regions in which the electrons are trapped.