Recent experimental studies of electron dephasing in metal and semiconductor mesoscopic structures

Abstract

In this review, we discuss the results of recent experimental studies of the low-temperature electron dephasing time (tau(phi)) in metal and semiconductor mesoscopic structures. A major focus of this review is on the use of weak localization, and other quantum-interference-related phenomena, to determine the value of tau(phi) in systems of different dimensionality and with different levels of disorder. Significant attention is devoted to a discussion of three-dimensional metal films, in which dephasing is found to predominantly arise from the influence of electron-phonon (e-ph) scattering. Both the temperature and electron mean free path dependences of tau(phi) that result from this scattering mechanism are found to be sensitive to the microscopic quality and degree of disorder in the sample. The results of these studies are compared with the predictions of recent theories for the e-ph interaction. We conclude that, in spite of progress in the theory for this scattering mechanism, our understanding of the e-ph interaction remains incomplete. We also discuss the origins of decoherence in low-diffusivity metal films, close to the metal-insulator transition. in which evidence for a crossover of the inelastic scattering, from e-ph to 'critical' electron-electron (e-e) scattering, is observed. Electron-electron scattering is also found to be the dominant source of dephasing in experimental studies of semiconductor quantum wires, in which the effects of both large- and small-energy-transfer scattering must be taken into account. The latter. Nyquist, mechanism is the stronger effect at a few kelvins, and may be viewed as arising from fluctuations in the electromagnetic back-ground, generated by the thermal motion of electrons. At higher temperatures, however, a crossover to inelastic e-e scattering typically occurs and evidence for this large-energy-transfer process has been found at temperatures as high as 30 K. Electron-electron interactions are also thought to play an important role in dephasing in ballistic quantum dots, and the results of recent experiments in this area are reviewed. A common feature of experiments, in both dirty metals and ballistic and quasi-ballistic semiconductors, is found to be the observation of an unexpected 'saturation' of the dephasing time at temperatures below a kelvin or so. The possible origins of this saturation are discussed, with an emphasis on recent experimental investigations of this effect.