Voltage fluctuations in multilead devices

The problem of voltage fluctuations in multilead devices can be formulated either in terms of fluctuating electric fields or fluctuating transmission amplitudes. We point out some subtleties regarding current conservation in the fluctuating-electric-field approach and then show that by treating the fluctuations in the transmission amplitudes exactly, the two approaches can be shown to be identical. We show that in the presence of a magnetic field the antisymmetric part of the conductivity has a finite divergence; however, when evaluated in perturbation theory, its effect is of higher order in the disorder and can be ignored. Finally, we present some results for voltage fluctuations in three-, four-, and six-lead devices. © 1988 The American Physical Society.