Pumping Current Noise in Ballistic Nanostructures: Acoustoelectric Current in a Point Contact

We consider current noise in a non biased ballistic nanostructure irradiated by an AC field, which is assumed to be a stationary random process to imitate time averaging in the experiment. The AC field creates a current, which contains DC and AC components, the latter vanishing after time averaging. Correspondingly, the correlator describing current noise has two contributions. The first contribution to it is responsible for the fluctuations of the DC current. These fluctuations happen because of electron inelastic transitions between scattering states. Transitions agitated by the thermal bath lead to a thermal noise spectrum, which disappears at zero temperature; its magnitude is renormalized compared to equilibrium. Transitions initiated by the AC field lead to a noise spectrum, which is a convolution of the thermal one and that of the AC field. The magnitude of this noise is proportional to the power of the AC field and is finite at zero temperature. The second contribution to the noise correlator is due to fluctuations of the AC current. This noise does not depend on temperature, and its spectrum reproduces that of the AC field.