NOISE SPECTRUM AND THE FLUCTUATION-DISSIPATION THEOREM IN MESOSCOPIC RINGS

A disordered one-dimensional metallic ring threaded by a magnetic flux is considered. The ensemble-averaged noise spectrum of the thermodynamic current fluctuations is calculated, and its dependence on flux, temperature, system size, and electron density is studied. Weak localization results are reproduced in the infinite-size limit and found not to contribute, to leading order, to the flux dependence. For a finite-size ring, the fluctuation-dissipation theorem is invoked to relate the noise spectrum to the real part of the ac conductance. The latter may be either a maximum or a minimum as a function of the flux, depending on the parity of the number of electrons. The results are discussed in view of previous studies of related problems. © 1991.