Effects of channel opening and disorder on the conductance of narrow wires

Abstract

The crossover from ballistic to diffusive transport in narrow two-dimensional conductors is studied as a function of Fermi energy and disorder. For an ordered sample, conductance quantization is confirmed. As the disorder is increased, the sharp conductance steps as a function of Fermi energy are rounded and preceded by pronounced dips. The origin of these dips is explained in terms of ‘‘level repulsion’’ between Lyapunov exponents of the total transfer matrix. For even larger disorder, the channel-opening signature in a given sample is obscured by universal conductance fluctuations. However, this structure can be restored, even for samples longer than the elastic mean free path, by ensemble averaging over different realizations of the disorder. The conditions for carrying out experimentally such an ensemble averaging are specified.