Dephasing of Electrons in Mesoscopic Metal Wires

• Published in: Physical review. B, Condensed matter and materials physics Condensed matter and materials physics, 2003, Vol.68
• Main Authors: Pierre, F., Gougam, A. B., Anthore, A., Pothier, H., Esteve, Daniel, Birge, Norman O.
• Format: Article
• Language: English
• Subjects: Condensed Matter; Mesoscopic Systems and Quantum Hall Effect; Physics
• ISSN: 1098-0121; 1550-235X
• DOI: 10.1103/physrevb.68.085413

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.