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.