Probing Interactions in Mesoscopic Gold Wires

Several recent experiments have demonstrated that the low-energy properties of quasiparticles in metallic thin films are sample-dependent. On the one hand, the power-law increase of the phase-coherence time with decreasing temperature, predicted by the theory of electron-electron interactions in diffusive wires [1], has been observed in several experiments [2, 3]. The energy exchange rates between electrons was found to be in agreement with this theory in experiments on silver wires [4]. On the other hand, the dephasing rate of quasiparticles was found to saturate at low temperature in a series of gold wires [5], and the energy exchange rate between quasiparticles in copper wires to display an energy dependence different from the predicted one [6]. We present here measurements on gold samples, in which the energy exchange rates have the same energy dependence as was observed in copper and have a magnitude even higher. In order to investigate the origin of this effect, we have performed resistance measurements on samples fabricated similarly. The logarithmic dependence of the resistance, the negative magnetoresistance at large field and the temperature dependence of the phase coherence time, which is constant between 8 K and 0.5 K and increases at lower temperature, suggest the presence of magnetic impurities, which might mediate electron-electron interactions.