Dephasing of Electrons in Mesoscopic Metal Wires

TL;DR

This study investigates electron dephasing in mesoscopic metal wires, revealing that magnetic impurities cause apparent saturation of phase coherence time, which aligns with electron-electron interaction theory in pure samples.

Contribution

It demonstrates that magnetic impurities at very low concentrations can cause apparent phase coherence saturation, clarifying previous experimental ambiguities.

Findings

Pure samples follow $T^{-2/3}$ dephasing law.

Magnetic impurities induce quasi saturation of $ au_{ ext{phi}}$.

Conductance oscillations increase with magnetic field.

Abstract

We have extracted the phase coherence time $\tau_{\phi}$ of electronic quasiparticles from the low field magnetoresistance of weakly disordered wires made of silver, copper and gold. In samples fabricated using our purest silver and gold sources, $\tau_{\phi}$ increases as $T^{-2/3}$ when the temperature $T$ is reduced, as predicted by the theory of electron-electron interactions in diffusive wires. In contrast, samples made of a silver source material of lesser purity or of copper exhibit an apparent saturation of $\tau_{\phi}$ starting between 0.1 and 1 K down to our base temperature of 40 mK. By implanting manganese impurities in silver wires, we show that even a minute concentration of magnetic impurities having a small Kondo temperature can lead to a quasi saturation of $\tau_{\phi}$ over a broad temperature range, while the resistance increase expected from the Kondo effect remains hidden by a large background. We also measured the conductance of Aharonov-Bohm rings fabricated using a very pure copper source and found that the amplitude of the $h/e$ conductance oscillations increases strongly with magnetic field. This set of experiments suggests that the frequently observed ``saturation'' of $\tau_{\phi}$ in weakly disordered metallic thin films can be attributed to spin-flip scattering from extremely dilute magnetic impurities, at a level undetectable by other means.