Quasi-ballistic conductance fluctuations and ergodic hypothesis

We study the conductance fluctuations in the quasi-ballistic transport regime by an analytical method based on the Lippmann-Schwinger equation and the Landauer formula. The contribution of single impurity scattering events, impurity potential fluctuations, multiple scattering between an impurity and sample boundaries as well as multiple scattering involving many impurities are discussed. The amplitude of the fluctuations cannot be measured by tuning the Fermi energy or an external magnetic field because the single impurity scattering events dominate the fluctuations, implying that the ergodic hypothesis breaks down in the quasi-ballistic transport regime. Absence of aperiodic oscillations in the experimental parametric conductance does not always mean an absence of defects in the sample. (C) 1998 Elsevier Science B.V. All rights reserved.