Abstract
We studied the low-temperature electron dephasing time$\tau_{\phi}$ in mesoscopic conductors: PdAu and PdAg thick films. The value of $\tau_{\phi}$ was determined by using weaklocalization effect in the three-dimensional disordered systems. Significant attention is devoted to a discussion ofthree-dimensional metal films, in which dephasing is found topredominantly arise from the influence of electron-phonondephasing, while the inelastic Nyquist electron-electron dephasing times can be neglected. Both the temperature and electron mean free path dependences of $\tau_{\phi}$ that result from electron-phonon scattering are found to be sensitive to the microscopic quality and degree of disorder in the sample. On the other hand, below a kelvin or near zero temperature, an unexpected saturation of the dephasing time is observed.In this work, We have measured the electron-phonon scatteringtimes $\tau_{ep}$ in Pd$_{60}$Ag$_{40}$ thick films that wereprepared by dc-sputtered films and rf-ones deposition techniques. In both series of samples, we find an anomalous $1/\tau_{ep}\propto T^{2}l$ temperature and disorder dependence, where $l$ is the electron elastic mean free path. Our result also reveals that the strength of the electron-phonon coupling is much stronger in the dc-than rf-sputtered films, suggesting that the electron-phonon interaction is not only sensitive to the total level of disorder, but is also sensitive to the microscopic quality of the disorder. The results of these studies are compared with the prediction of recent theories for electron-phonon interaction. We conclude that in spite of progress in the theory for this scattering mechanism, our understanding of the electron-phonon interaction remains incomplete. In addition, we have studied the effect of thermal annealing on electron dephasing times $\tau_{\phi}$ in three-dimensional polycrystalline metals. Measurements are performed on as-sputtered and annealed Pd$_{50}$Au$_{50}$ films. We find that $\tau_{\phi}$ possesses an extremely weak temperature dependence as $T \rightarrow 0$. Our results show that the effect of annealing is non-universal, and it depends strongly on the amount of disorder quenched in the microstructures during deposition. The observed saturation behavior of $\tau_{\phi}$ and effect of annealing on $\tau_{\phi}^{0}$ cannot be easily explained by magnetic scattering mechanism or scattering due to two-level systems. In PdAu and PdAg thick films,We find $\tau_{\phi}^{0} \propto D^{-1}$, where $D$ is the electron diffusion constant. This result is certainly not due to microwave noise, because microwave-noise dephasing should result in a $\tau_{\phi}^{0} \propto D^{-1/3}$ dependence in three dimensions as predicted by Alshuler et al. The problem of zero-temperature dephasing still remains controversial and inconclusive both in experiment and theory.