The electron shot noise in a multiprobe mesoscopic conductor can have a nonlinear dependence on the strength of driving bias voltage. This paper presents a theoretical formulation for the nonlinear noise spectra. We pay special attention to maintain gauge invariance at the nonlinear level. At small but finite voltages, explicit expressions for nonlinear noise spectra, expanded order by order in the bias, have been derived. In the wideband limit, a closed-form solution of the noise spectra for finite voltages is obtained.

• Received 19 January 1999

DOI:https://doi.org/10.1103/PhysRevB.60.16900