Conductance fluctuations in small disordered conductors: Thin-lead and isolated geometries

Abstract

We extend the analysis of conductance fluctuations in small disordered metallic systems beyond the conventional thick-lead geometry to thin-lead and isolated geometries. We find that, for the thin-lead geometry, the conductance fluctuations are still given by the ‘‘universal’’ value $e^2$/h, independent of the lead width. In the isolated geometry, the conductance fluctuation is enhanced by a factor ($L_{\mathrm{in}/\mathrm{L}{)}^2\mathrm{\gg }1}$ over $e^2$/h. The typical distance between consecutive peaks and valleys in the structure of conductance fluctuations, both as a function of external magnetic field and of chemical potential, is found to be dramatically reduced in both of these restrictive geometries.