In this review, we discuss the results of recent experimental studies of the low-temperature electron dephasing time (τφ) 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 τφ 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 τφ 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 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 3 Authors to whom any correspondence should be addressed.

https://iopscience.iop.org/article/10.1088/0953-8984/14/18/201/pdf

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

We study the transport of ultracold atoms in a tight optical lattice. For identical fermions the system is insulating under an external force while for bosonic atoms it is conducting. This reflects the different collisional properties of the particles and reveals the role of interparticle collisions in establishing a macroscopic transport in a perfectly periodic potential. Also in the case of fermions we can induce a transport by creating a collisional regime through the addition of bosons. We investigate the transport as a function of the collisional rate and observe a transition from a regime in which the mobility increases with increasing collisional rate to one in which it decreases. We compare our data with a theoretical model for electron transport in solids introduced by Esaki and Tsu.

https://arxiv.org/pdf/cond-mat/0311261.pdf

Collisionally induced transport in periodic potentials.

The bismuth microbolometer is a simple, easily made detector suitable for use throughout the far-infrared, which has been integrated with a variety of planar antennas. The general thermal properties of these devices and some of the constraints on bolometer materials are discussed. The fabrication and performance of several different types of microbolometers and microthermocouples are described.

Far-infrared microbolometer detectors

The incorporation of phosphorus in silicon is studied by analyzing phosphorus δ-doped layers using a combination of scanning tunneling microscopy, secondary ion mass spectrometry, and Hall effect measurements. The samples are prepared by phosphine saturation dosing of a Si(100) surface at room temperature, a critical annealing step to incorporate phosphorus atoms, and subsequent epitaxial silicon overgrowth. We observe minimal dopant segregation (∼5 nm), complete electrical activation at a silicon growth temperature of 250 °C and a high two-dimensional electron mobility of ∼102 cm2/V s at a temperature of 4.2 K. These results, along with preliminary studies aimed at further minimizing dopant diffusion, bode well for the fabrication of atomically precise dopant arrays in silicon such as those found in recent solid-state quantum computer architectures.

Encapsulation of phosphorus dopants in silicon for the fabrication of a quantum computer

A new formalism is proposed to correct with accuracy the matrix effects in x-ray fluorescence (XRF) analysis It has been deduced from Sherman's equations and includes a new algorithm between concentration and intensity, theoretically exact, and explicit expressions permitting the calculation of αij and ρij coefficients that correct for absorption and enhancement effects, respectively In other words, the concept of correction coefficients is established on a solid theoretical basis In the second part, it will be shown how to adapt this new formalism to practical situations From an estimate of composition calculated by the Claisse–Quintin algorithm and an appropriate calibration, the new algorithm is used to refine the estimated composition for greater accuracy This last approach is equivalent to the ‘fundamental parameters’ method but is presented in a simpler version adaptable to any mini-computer

Fundamental algorithm between concentration and intensity in XRF analysis 1—theory

Low-temperature electron transport in Si with an MBE-grown Sb δ layer

The temperature and magnetic-field dependences of the resistance of Si/SiGe heterojunctions with hole-type conductivity are investigated. It is shown that the features of these dependences are due to a manifestation of quantum interference effects — weak localization of the mobile charge carriers, and the hole–hole interaction in the two-dimensional electron system. On the basis of an analysis of the quantum interference effects, the temperature dependence of the dephasing time of the wave function of the charge carrier is determined: τφ=6.6×10−12T−1 s. This dependence τφ∝T−1 must be regarded as a manifestation of hole–hole scattering processes in the two-dimensional electron system. The contribution to the magnetoresistance from the hole–hole interaction in the Cooper channel is extracted, and the corresponding interaction constant λ0C≈0.5 is found.

Quantum effects in hole-type Si/SiGe heterojunctions

, Phone: +380-57-340-22-23, Fax: +380-57-3410963The magnetoresistance and electrical resistivity of nitrogen-doped multi-walled carbon nanotubes (N-MWCNTs) werestudied in the temperature range of 1.6–100.3 and 1.6–286K,respectively, using a standard four-probe technique. The pos-sible mechanisms of the observed effects are discussed indetail.

Magnetoresistance and electrical resistivity of N‐doped multi‐walled carbon nanotubes at low temperatures

Temperature variation of the time of inelastic electron relaxation in disordered bismuth films.

The paper reports on an investigation of the electric resistance as a function of temperatureT, magnetic fieldH, and applied voltageV in granular indium films when approaching the metal-insulator transition (MIT) due to increased thickness of the oxide layers between granules. The dependences are shown to be governed atT≤5 K by competition of the hopping conductivity and the Josephson tunneling of electrons, sometimes giving rise to a resistance minimum inR(T) associated with superconductivity. It was also found that even when the intergranular Josephson tunneling is totally suppressed, transition of granules to the superconducting state influences essentially the dependencesR(T, H), changing the functional form ofR(T) and resulting in anomalously high negative magnetoresistance. This is shown to stem from the change of the character of activated electron tunneling as the granules become superconducting.

Yu. F. Komnik

Papers

Low-temperature electron transport in Si with an MBE-grown Sb δ layer

Quantum effects in hole-type Si/SiGe heterojunctions

Magnetoresistance and electrical resistivity of N‐doped multi‐walled carbon nanotubes at low temperatures

Temperature variation of the time of inelastic electron relaxation in disordered bismuth films.

Superconductivity effects near the metal-insulator transition in granular indium films