The Boltzmann--Langevin approach: A simple quantum-mechanical derivation

We present a simple quantum-mechanical derivation of correlation function of Langevin sources in the semiclassical Boltzmann--Langevin equation. The specific case of electron--phonon scattering is considered. It is shown that the assumption of weak scattering leads to the Poisson nature of the scattering fluxes.Comment: 4 pages, 1 figure, invited contribution to special issue in Physica E on "Frontiers in quantum electronic transport - in memory of Markus B\"uttiker

Comment on "Universality of the 1/3 shot-noise suppression factor in nondegenerate diffusive conductors"

We argue that the nearly 1/3 suppression of shot noise in nondegenerate diffusive contacts recently obtained by Gonzalez et al. (cond-mat/9803372) is due to the specific choice of the energy-independent elastic scattering time.Comment: 2 pages, RevTex, no figure

Electron-electron scattering and conductivity of long multimode channels

The electron-electron scattering increases the resistance of ballistic many-mode channels whose width is smaller than their length. We show that this increase saturates in the limit of infinitely long channels. Because the mechanisms of angular relaxation of electrons in three and two dimensions are different, the saturation value of the correction to the resistance is temperature-independent in the case of three-dimensional channels and is proportional to the temperature for two-dimensional ones. The spatial behavior of electron distribution in the latter case is described by an unusual characteristic length.Comment: 8 pages, 3 figure

How an incorrect transition from finite to infinite 2D conductor may result in a false negative relaxation

We consider the relaxation of a uniform current in a planar 2D conductor with account taken of electromagnetic retardation effects. If the 2D conductivity is larger than the speed of light, the straightforward solution for an infinite plane gives a negative relaxation rate. However if one starts from a conducting cylinder of finite radius and then increases it to infinity, the relaxation rate just tends to zero while remaining positive. We suggest that recent unusual plasmon-dispersion curves obtained by V. A. Volkov and A. A. Zabolotnykh [arXiv:1605.00430] result from the incorrect finite-to-infinite transition.Comment: Typo in Eq. 5 correcte

Nonlinear conductivity of diffusive normal-metal contacts

Metal microbridges with a high impurity content and shorter than the energy relaxation length are considered. Their conductance is calculated with allowance made for the Coulomb electron-electron interaction. It is shown that nonequilibrium electrons in the microbridges gives rise to a nonlinear current-voltage characteristic (published in Physics Letters A, 1994).Comment: 3 pages, 2 eps figure

Frequency-dependent shot noise in long disordered SNS contacts

The shot noise in long diffusive SNS contacts is calculated using the semiclassical approach. At low frequencies and for purely elastic scattering, the voltage dependence of the noise is of the form S_I = (4\Delta + 2eV)/3R. The electron-electron scattering suppresses the noise at small voltages resulting in vanishing noise yet infinite dS_I/dV at V = 0. The distribution function of electrons consists of a series of steps, and the frequency dependence of noise exhibits peculiarities at \omega = neV, \omega = neV - 2\Delta, and \omega = 2\Delta - neV for integer n.Comment: 4 pages, 4 eps figure

Electron-electron scattering and magnetoresistance of ballistic microcontacts

Using a semiclassical Boltzmann equation, we calculate corrections to the Sharvin conductance of a wide 2DEG ballistic contact that result from an electron--electron scattering in the leads. These corrections are dominated by collisions of electrons with nearly opposite momenta that come from different reservoirs. They are positive, increase with temperature, and are strongly suppressed by a magnetic field. We argue that this suppression may be responsible for an anomalous positive magnetoresistance observed in a recent experiment.Comment: 10 pages, 8 figures, published versio

Charge and spin current in a quasi-one-dimensional quantum wire with spin-orbit coupling

We show that Rashba spin-orbit coupling may result in an energy gap in the spectrum of electrons in a two-mode quantum wire if a suitable confining potential is chosen. This leads to a dip in the conductance and a spike in the spin current at the corresponding position of the Fermi level. Therefore one may control the charge and spin currents by means of electrostatic gates without using magnetic field or magnetic materials.Comment: 5 pages, 5 figures, published versio

Non-universal shot noise in quasiequilibrium spin valves

We show that the breakdown of the Wiedemann-Franz law due to electron--electron scattering in diffusive spin valves may result in a strong suppression of the Fano factor that describes the ratio between shot noise and average current. In the parallel configuration of magnetizations, we find the universal value $\sqrt{3}/4$ in the absence of a normal-metal spacer layer, but including the spacer leads to a non-monotonous suppression of this value before reaching back to the universal value for large spacer lengths. On the other hand, in the case of an antiparallel configuration with a negligibly small spacer, the Fano factor is $\sqrt{3 (1-P^2)}/4$, where $P$ denotes the polarization of the conductivities. For $P\rightarrow \pm 1$, the current through the system is almost noiseless.Comment: 5+ pages, 5 figures, including a short appendi

Conductance of Interacting Quasi-One-Dimensional Electron Gas with a Scatterer

We calculate the conductance of a quantum wire with two occupied subbands in a presence of a barrier taking into account the interaction between electrons. We extend the renormalization-group equation for the scattering matrix of the barrier to the case of intersubband interactions, find its fixed points, and investigate their stability. Depending on the interaction parameters, the conductance may be equal to 0, $e^2/h$, or $2e^2/h$ per spin projection. In some parameter ranges, two stable fixed points may coexist, so the ultimate conductance depends on the properties of the bare barrier. For spinful electrons, the conductance of the wire may nonmonotonically depend on the Fermi level and temperature.Comment: 9 pages, 4 figures, published versio