Experimental comparison of the phase-breaking lengths in weak localization and universal conductance fluctuations

The observation of quantum transport phenomena in metals is limited by the eventual loss of phase coherence of the conduction electrons on the length scale $L_{\phi }.$ We address the question of whether $L_{\phi }$ is the same in the context of different quantum transport phenomena. Specifically, we have measured $L_{\phi }$ from two different experiments on the same sample. The experiments are magnetoresistance and $1/f$ noise versus magnetic field, and the samples are thin-Ag films in the quasi-two-dimensional regime. We determine $L_{\phi }$ from fits of the magnetoresistance data to weak-localization theory (WL), and from fits of the noise versus magnetic field to universal conductance fluctuation theory (UCF). We find that the two values of $L_{\phi }$ are the same at temperatures above about 10 K, but that $L_{\phi }$ in the UCF experiment is shorter than that in the WL experiment at lower temperatures. This result is consistent with a recent theoretical discussion of quasielastic electron-electron scattering in disordered metals.