On the ‘Anomalous’ Resurgence of Shot Noise in Long Conductors

There has been renewed interest in the physics of the so-called ‘crossover’ for current fluctuations in mesoscopic conductors, most recently involving the possibility of its appearance in the passage to the macroscopic limit. Shot noise is normally absent from solid-state conductors in the large, and its anomalous resurgence there has been ascribed to a rich interplay of drift, diffusion, and Coulomb screening. We demonstrate that essentially the same rise in shot noise occurs in a much less complex system: the Boltzmann-Drude-Lorentz model of a macroscopic, uniform gas of strictly non-interacting carriers. We conclude that the ‘anomalous crossover’ is a manifestation of simple kinetics. Poissonian carriers, if driven by a high enough field, cross the sample faster than any scattering time, thus fulfilling Schottky’s condition for ideal shot noise.