In this review, we discuss the results of recent experimental studies of the low-temperature electron dephasing time (τ φ) 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 τ φ 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 τ φ 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. Electronelectron 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 background, 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

We have studied the carrier transport in two topological insulator (TI) Bi2Te3 microflakes between 0.3 and 10 K and under applied backgate voltages (VBG). Logarithmic temperature dependent resistance corrections due to the two-dimensional electron-electron interaction effect in the presence of weak disorder were observed. The extracted Coulomb screening parameter is negative, which is in accord with the situation of strong spin-orbit scattering as is inherited in the TI materials. In particular, positive magnetoresistances (MRs) in the two-dimensional weak-antilocalization (WAL) effect were measured in low magnetic fields, which can be satisfactorily described by a multichannelconduction model. Both at low temperatures of T < 1 K and under high positive VBG, signatures of the presence of two coherent conduction channels were observed, as indicated by an increase by a factor of ≈ 2 in the prefactor which characterizes the WAL MR magnitude. Our results are discussed in terms of the (likely) existence of the Dirac fermion surface states, in addition to the bulk states, in the three-dimensional TI Bi2Te3 material.

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We have systematically measured the electrical resistivities and thermopowers of transparent tin-doped indium oxide films. We found that the resistivities obey the Bloch-Grüneisen law between 25 and 300K, whereas below 25K, the resistivities slightly increase logarithmically with the decreasing temperature due to the weak-localization and electron-electron interaction effects. The thermopowers are negative and decrease linearly with temperature from 300K down to 1.8K. Our results strongly indicate that the tin-doped indium oxide films behave as a good, free-electron-like conductor while being transparent.

Nearly 3 orders of magnitude enhancement in the Hall coefficient is observed in Cu x -͑SiO 2 ͒ 12x granular films. This large enhancement of the Hall coefficient not only is significantly larger than the prediction of the classical percolation theory, but also occurs at a metal concentration identified to be the quantum percolation threshold. Measurements of the electron dephasing length and magnetoresistance, plus the TEM characterization of microstructures, yield a physical picture consistent with the mechanism of the local quantum interference effect. DOI: 10.1103/PhysRevLett.86.5562 PACS numbers: 72.20.My, 71.30. +h, 72.80.Tm, 73.50.Jt As a basic material constant, the Hall coefficient is generally indicative of the density and sign of the charge carriers. Thus, in granular metals, as the metal concentration decreases, the lower carrier density is expected to yield an enhanced Hall coefficient which peaks at the percolations threshold with a factor of ϳ30 for ϳ1 mm thick films [1,2]. Recently, however, it was found that in the magnetic ͑NiFe͒-SiO 2 , and Fe-SiO 2 granular films [2-5], the extraordinary Hall coefficient was enhanced by a factor of 10 4 when the metal volume fraction is close to x 0.53 (the classical percolation threshold). An especially intriguing feature of this discovery is that, even after magnetic saturation, the ordinary Hall coefficient was still observed to increase by almost 3 orders of magnitude [4], suggesting a magnetic-independent mechanism could be operative.In this Letter, we focus on the origin of the ordinary giant Hall effect (GHE) by studying the nonmagnetic Cu-SiO 2 granular system. We find the same 3 orders of magnitude enhancement in the Hall coefficient. By carrying out measurements on the electron dephasing length and the magnetoresistance (MR), and by characterizing our samples by transmission electron microscope (TEM) pictures, we find the Hall coefficient to peak at the quantum percolation threshold. Based on the picture that inhomogeneities (due to the small substructures) inside a dephasing length would necessarily cause local quantum interference and thereby modify the effective local properties, we show that all experimental data can be quantitatively accounted for within this simple framework. In particular, when the small substructures are suppressed through annealing, the GHE is shown to disappear, in agreement with the theoretical prediction [6].Cu-SiO 2 granular films with different metal volume fractions were fabricated by using the cosputtering technique with a glass or Kapton substrate, at a temperature of 50 ± C. The base pressure of the chamber was kept below 2 3 10 27 Torr. The films deposited on the glass were used for transport measurements and the films on Kapton were for composition determination. The metal volume fraction x for all the films was obtained from energydispersive x-ray spectroscopy analysis. The dc resistance was measured by using the standard four-probe technique, and the Hall resistance was measured by using the five-contacts me...