Influence of Magnetic Field on Effective Electron-electron Interactions in a Copper Wire

In metallic wires, electron-electron interactions lead to quasi-elastic scattering, which modifies the electron phase-coherence time, and to inelastic scattering, which redistributes energy between electrons. Several recent experiments have shown that these properties can be sampledependent 1,2. We have found furthermore that the low-temperature saturation of the phasecoherence time τφ of quasiparticles, observed in several experiments, is correlated with an anomalous dependence on the exchanged energy ε of K(ε), a function proportional to the averaged squared interaction between two quasiparticles. The theoretical predictions, for pure Coulomb interactions , τφ ∝ T −2/3 and K(ε) ∝ ε−3/2, were observed in silver wires , whereas a “saturating” τφ and K(ε) ∝ ε −2 were systematically found in copper wires5,6. In gold wires in which the presence of a large concentration of magnetic impurities (∼ 50 ppm of iron) could be assessed, K(ε) was also found to behave as ε, with a particulary large prefactor . On the theoretical side, it was recently understood that scattering by magnetic impurities, which limits the phase coherence time on a large range of temperature, can also provide another channel for energy exchange between quasiparticles 8,9,10. In order to probe if magnetic impurities indeed play a role in copper wires, we have measured the magnetic field dependence of the energy exchange rate.