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K. E. Nagaev

Publications and source records attributed to K. E. Nagaev.

At least 19 recordsLinked to original sources
arXiv2022

Electron--electron scattering and conductivity of disordered systems with Galilean-invariant spectrum

The electron--electron scattering does not affect the electrical current in Galilean--invariant systems. We show that nevertheless electron--electron collisions may contribute to the electric resistivity of systems with parabolic spectrum provided that they have multiply connected Fermi surface and there is an additional mechanism of scattering. To this end, we calculate the resistivity of a two-dimensional electron gas with two filled transverse subbands in a presence of electron--electron and impurity scattering. Though the collisions between the electrons do not directly affect the current in such systems, they cause a redistribution of the electrons between the Fermi contours, which results in a noticeable change of resistivity for realistic mechanisms of impurity scattering.

cond-mat.mes-hall↗
arXiv2021

Finite-frequency response of Rasba electron gas with two-particle scattering

Two-dimensional systems with Rashba spin-orbit coupling are not Galilean invariant and therefore electron--electron collisions in them may affect the current. However when taken alone, they cannot ensure a nonzero dc resistivity, so their effects are masked by impurity scattering. Here we calculate the related finite-frequency response and show that the electron--electron scattering in clean Rashba conductors decreases the Drude weight while resulting in a finite dissipative component of the response outside of the Drude peak.

cond-mat.mes-hall↗
arXiv2020

Electron-electron scattering and transport properties of spin-orbit coupled electron gas

We calculate the electrical and thermal conductivity of a two-dimensional electron gas with strong spin--orbit coupling in which the scattering is dominated by electron--electron collisions. Despite the apparent absence of Galilean invariance in the system, the two-particle scattering does not affect the electrical conductivity above the band-crossing point where both helicity bands are filled. Below the band-crossing point where one helicity band is empty, switching on the electron--electron scattering leads only to a limited decrease of the electrical conductivity, so that its high-temperature value is independent of the scattering intensity. In contrast to this, thermal conductivity is not strongly affected by the spin-orbit coupling and exhibits only a kink as the Fermi level passes through the band-crossing point.

cond-mat.mes-hall↗
arXiv2020

Two-particle scattering and resistivity of Rashba electron gas

We calculate the electrical resistivity of a two-dimensional electron gas that results from two-particle collisions and strong Rashba spin-orbit coupling. In the absence of impurities, two-particle collisions do not contribute to resistivity. When combined with impurity scattering, the two-particle correction to the resistivity is proportional to the square of temperature $T$ if only the lower helicity band is filled, but the $T^2$ term vanishes if the Fermi level is above the Dirac point.

cond-mat.mes-hall↗
arXiv2020

Sign reversal of nonlocal response due to electron collisions

Electron-electron collisions are known to cause a nonlocal voltage drop in a presence of current flow. The semi-phenomenological theory predicts this drop to be opposite to the direction of the current in the ballistic regime. We use a microscopic approach and show that the sign of this drop may be of both signs depending on the temperature and the distance between the source and probe contacts. The change of sign corresponds to the change of the dominant scattering process from head-on collisions to backward scattering of electrons. Our results agree with the experimental data.

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arXiv2018

Noise in the helical edge channel anisotropically coupled to a local spin

We calculate the frequency-dependent shot noise in the edge states of a two-dimensional topological insulator coupled to a magnetic impurity with spin $S=1/2$ of arbitrary anisotropy. If the anisotropy is absent, the noise is purely thermal at low frequencies, but tends to the Poissonian noise of the full current $I$ at high frequencies. If the interaction only flips the impurity spin but conserves those of electrons, the noise at high voltages $eV\gg T$ is frequency-independent. Both the noise and the backscattering current $I_{bs}$ saturate at voltage-independent values. Finally, if the Hamiltonian contains all types of non-spin-conserving scattering, the noise at high voltages becomes frequency-dependent again. At low frequencies, its ratio to $2eI_{bs}$ is larger than 1 and may reach 2 in the limit $I_{bs}\to 0$. At high frequencies it tends to 1.

cond-mat.mes-hall↗
arXiv2018

Spin-orbit coupling and resonances in the conductance of quantum wires

We investigate a possibility of pair electron-electron e-e collisions in a ballistic wire with spin-orbit coupling and only one populated mode. Unlike in a spin-degenerate system, a combination of spin-splitting in momentum space with a momentum-dependent spin-precession opens up a finite phase space for pair e-e collisions around three distinct positions of the wire's chemical potential. For a short wire, we calculate corresponding resonant contributions to the conductance, which have different power-law temperature dependencies, and, in some cases, vanish if the wire's transverse confinement potential is symmetric. Our results may explain the recently observed feature at the lower conductance plateau in InAs wires.

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arXiv2018

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.

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arXiv2018

AC Response of the Edge States in a Two-Dimensional Topological Insulator Coupled to a Conducting Puddle

We calculate an AC response of the edge states of a two-dimensional topological insulator, which can exchange electrons with a conducting puddle in the bulk of the insulator. This exchange leads to finite corrections to the response of isolated edge states both at low and high frequencies. By comparing these corrections, one may determine the parameters of the puddle.

cond-mat.mes-hall↗
arXiv2017

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.

cond-mat.mes-hall↗
arXiv2016

Current noise generated by spin imbalance in presence of spin relaxation

We calculate current (shot) noise in a metallic diffusive conductor generated by spin imbalance in the absence of a net electric current. This situation is modeled in an idealized three-terminal setup with two biased ferromagnetic leads (F-leads) and one normal lead (N-lead). Parallel magnetization of the F-leads gives rise in spin-imbalance and finite shot noise at the N-lead. Finite spin relaxation results in an increase of the shot noise, which depends on the ratio of the length of the conductor ($L$) and the spin relaxation length ($l_s$). For $L\gg l_s$ the shot noise increases by a factor of two and coincides with the case of the anti-parallel magnetization of the F-leads.

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arXiv2016

Shot noise in the edge states of 2D topological insulators

We calculate the resistance and shot noise in the edge states of a 2D topological insulator that result from the exchange of electrons between these states and conducting puddles in the bulk of the insulator. The two limiting cases where the energy relaxation is either absent or very strong are considered. A finite time of spin relaxation in the puddles is introduced phenomenologically. Depending on this time and on the strength of coupling between the edge states and the puddles, the Fano factor $F=S_I/2eI$ ranges from 0 to 1/3, which is in an agreement with the available experimental data.

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arXiv2015

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.

cond-mat.stat-mech↗
arXiv2014

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.

cond-mat.mes-hall↗
arXiv2014

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.

cond-mat.mes-hall↗
arXiv2013

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.

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