Time-dependent universal conductance fluctuations and coherence in AuPd and Ag

Abstract

Quantum transport phenomena allow experimental assessment of the phase coherence information in metals. We report quantitative comparisons of coherence lengths inferred from weak localization magnetoresistance measurements and time-dependent universal conductance fluctuation data. We describe these two measurements and their analysis. Strong agreement is observed in both quasi-two-dimensional and quasi-one-dimensional (1D) AuPd samples, a metal known to have high spin-orbit scattering. However, quantitative disagreement is seen in quasi-1D Ag wires below $10\phantom{\rule{0.3em}{0ex}}\mathrm{K}$, a material with intermediate spin-orbit scattering. We consider explanations of this discrepancy, with particular emphasis on the theoretical expressions used to analyze the field dependence of the conductance fluctuations. We also discuss the mechanism of the suppression of conductance fluctuations at high drive levels, and dephasing mechanisms at work in these systems.