Mechanism of Universal Conductance Fluctuations

TL;DR

This paper analyzes the spectral nature of universal conductance fluctuations, revealing that their Fourier spectrum is discrete and resembles white noise, challenging the assumption of complete randomness at large scales.

Contribution

It provides an accurate Fourier analysis showing that conductance fluctuations have a discrete spectrum, supporting a superposition of incommensurate harmonics rather than random oscillations.

Findings

Spectrum is purely discrete, consistent with superposition of incommensurate harmonics.

Spectrum resembles white noise, indicating near-randomness at large scales.

Supports alternative scenario to the completely random oscillations model.

Abstract

Universal conductance fluctuations are usually observed in the form of aperiodic oscillations in the magnetoresistance of thin wires as a function of the magnetic field B. If such oscillations are completely random at scales exceeding \xi_B, their Fourier analysis should reveal a white noise spectrum at frequencies below \xi_B^{-1}. Comparison with the results for 1D systems suggests another scenario: according to it, such oscillations are due to the superposition of incommensurate harmonics and their spectrum should contain discrete frequencies. An accurate Fourier analysis of the classical experiment by Washburn and Webb reveals a purely discrete spectrum in agreement with the latter scenario. However, this spectrum is close in shape to the discrete white noise spectrum whose properties are similar to a continuous one.