Spectral Analysis of Universal Conductance Fluctuations

Universal conductance fluctuations are usually observed in the form of aperiodic oscillations in the magnetoresistance of thin wires under variation of the magnetic field B . A Fourier analysis of aperiodic oscillations observed in the classical experiments by Webb and Washburn reveals a practically discrete spectrum in agreement with the scenario based on the analogy with one-dimensional systems, according to which conductance fluctuations are due to the superposition of incommensurate harmonics. A more detailed analysis reveals the existence of a continuous component, whose smallness is explained theoretically. A lot of qualitative results are obtained that confirm the presented picture: the distribution of phases, frequency differences, and the growth exponents is consistent with theoretical predictions; discrete frequencies weakly depend on the processing procedure; and the discovered shift oscillations confirm the analogy with one-dimensional systems. Microscopic estimates show that the results obtained are consistent with the geometrical dimensions of the sample.