arXiv subjects

P. S. Alekseev

Publications and source records attributed to P. S. Alekseev.

At least 19 recordsLinked to original sources

arXiv2026

Hydrodynamics of two-dimensional electrons due to scattering by disorder

The hydrodynamic regime of electron transport, induced by fast inter-electron collisions, was discovered in high-quality nanostructures in recent ten years. However, signs of hydrodynamic transport, primarily, the giant negative magnetoresistance, were observed even at very low temperatures, when electron-electron scattering is too weak to affect the transport. To address this puzzle, here we develop a theory of mixed, hydrodynamic and non-Markovian, magnetotransport of two-dimensional electrons at zero temperature in samples with weak but still important disorder. Namely, we account for both the memory effects at electron scattering by localized defects in magnetic field and an unconventional viscosity effect due to electron scattering by defects in bulk and by rough sample edges. Solution of the model yields a strong negative magnetoresistance, which exhibits at zero magnetic field a sharp maximum in narrower samples or a blunt maximum in wider samples. This and other our results explain various properties of the giant negative magnetoresistance observed on ultra-high-quality GaAs quantum wells, thereby we apparently reveal the nature of low-temperature magnetotransport in these systems.

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arXiv2026

Hall effect in viscous flows of two-dimensional electrons in samples with edges of arbitrary roughness

In ultra-clean conductors, fast inter-particle collisions can lead to the formation of a viscous electron fluid and realization of the hydrodynamic transport regime. Here we develop a theory of hydrodynamic magnetotransport of two-dimensional (2D) electrons in samples with low densities of defects and edges of arbitrary roughness. Within our model the roughness is described by a single parameter with the dimension of speed in the boundary conditions on sample edges. The electron-fluid flow profiles in long samples, as well as the corresponding longitudinal and Hall resistances, are calculated. The contribution to the Hall resistance associated with the relaxation processes exhibits a saturation in the limit of high magnetic field and a minimum as a function of the magnetic field for sufficiently rough edges. The minimum disappears as the edge roughness decreases or the sample width and bulk scattering by defects increase. These properties of the Hall resistance can serve as the signs to identify the hydrodynamic regime of electron transport in experiments and can be used to determine its parameters, in particular, the degree of edge roughness.

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arXiv2026

Kinetic coefficients of two-dimensional electrons with strong Zeeman splitting

In modern nanostructures with very low defect densities, has recently been realized a hydrodynamic regime of electric transport, in which two-dimensional (2D) electrons form a viscous fluid due to frequent electron-electron collisions. Many bright transport phenomena have been observed in these systems. Of particular interest are two-component hydrodynamic electron systems, where a richer variety of phenomena becomes possible, than in one-component systems. A simplest way to implement and control a two-component 2D electron system is to place a structure with 2D electrons in a magnetic field with a large component in the 2D plane, that leads to a Zeeman splitting of the electron energy spectrum into two subbands. Here we develop a microscopic model of hydrodynamic transport in such system. By solving the kinetic equation, we calculate the electron-electron relaxation rates of the first and second angular harmonics of the two-component distribution function. Then we derive the hydrodynamic balance equations with the kinetic coefficient containing these rates. Namely, are taken into account the shear viscosity in each fluid component and the effect of the friction between the two components. The last leads to equalization of the hydrodynamic velocities in the two subbands. The obtained equations can be used to explain the results of puzzling magnetotransport experiments in ultra-pure nanostructures in a strong oblique magnetic field.

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arXiv2026

Non-Newtonian two-dimensional electron fluid in magnetic field

We develop a theory of the non-Newtonian regime of non-linear hydrodynamic magnetotransport of a two-dimensional (2D) viscous electron fluid controlled by the local Joule heating. In this mechanism, the electron shear viscosity in magnetic field becomes a non-monotonic function of the gradient of the hydrodynamic velocity due to the flow-induced increase of the electron temperature. We derive and solve the corresponding non-linear hydrodynamic equations for a velocity profile in a Poiseuille-like flow geometry. We demonstrate that the calculated magnetoresistance of such flow well explains the differential magnetoresistance observed for 2D electrons in various samples of ultra-high-quality GaAs quantum wells at high currents. We conclude that the non-linear regime of 2D electron fluid flows is such systems is realized via formation of a 2D non-Newtonian electron fluid, related to non-linearity in viscosity, but not via convective ``kinematic-induced'' effects, as it takes place in ordinary uncharged fluids.

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arXiv2026

Flow bistability in non-Newtonian electron fluid

Modern two dimensional conductors with low defect densities and strong electron-electron scattering are favorable platforms for formation of a viscous fluid of conduction electrons. Electric properties of these systems are determined by the hydrodynamic regime of charge transport distinguished by many experimental signatures: a decrease in sample resistance with increasing temperature (the Ghurzhi effect), strong negative magnetoresistance and others. Here we consider the flow of 2D electron fluid in the nonlinear regime characterized by non-Newtonian viscosity which depends on spatial gradients of hydrodynamic velocity. We derive a simplified version of the dynamic equations for the non-Newtonian electron fluid and consider the specific underlying mechanism associated with local electron heating. Recent works have demonstrated that this may be one of the main mechanisms for nonlinearity in 2D electron fluids. We show that in a certain range of parameters, the two steady-state flow configurations coexist for the narrow channel geometry, and this bistability leads to an S-shaped current-voltage characteristic. By solving the derived time-dependent dynamic equations, we trace the transient response to a step variation of the longitudinal voltage and demonstrate how the current switching and hysteresis occur in samples with the non-Newtonian electron fluid.

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arXiv2025

Analytical model for non-linear magnetotransport in viscous electron fluid

We develop an analytical theoretical model for non-linear hydrodynamic magnetotransport of two-dimensional (2D) electron fluid with strong pair correlations in the electron dynamics. Within classical kinetics of 2D electrons, such correlations are described as subsequent ``extended'' collisions of the same electrons, temporarily joined in pairs. Corresponding correlation-induced retarded terms in the fluid dynamic equations can be described for slow flows as the dependence of the electron fluid viscosity on the flow velocity gradient, that is Non-Newtonian behavior of the fluid. We analytically calculate flow profiles in long samples in a stationary highly non-linear regime and the corresponding magnetoresistance. Pair correlations lead to a characteristic non-monotonic dependence of the differential resistance on magnetic field. We compare our results with experimental data on non-linear magnetotransport of high-purity GaAs quantum wells; we conclude that our model can be responsible for a part of the observed features of the differential magnetoresistance.

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arXiv2025

Highly correlated two-dimensional viscous electron fluid in moderate magnetic fields

Magnetotransport phenomena often provide critically important information about two-dimensional (2D) electron systems. For example, the independence of magneto-photo-resistance of 2D electrons in best-quality quantum wells on the polarization helicity of incident radio-frequency radiation have been treated as a puzzling effect, which is important for characterization of these systems, but had no well-established explanation up to now. Here we develop a phenomenological model of dynamics of a highly correlated 2D electron fluid in moderate magnetic fields, in which shear viscosity and the memory effects in inter-particle interaction are crucial. In this system, successive collisions of electrons joined in pairs (that is, the pair correlations in time) turn out to be as important as uncorrelated collisions of statistically independent electrons. The resulting photoresistance exhibits an irregular shape of magnetooscillations, the absence of the dependence on the helicity of the circular polarization of radiation, and a giant peak near the doubled cyclotron frequency. All these effects were observed in experiments on best-quality GaAs quantum wells in moderate magnetic fields at low temperatures. Although the most general conditions of applicability of the developed phenomenological model is not fully clarified at now, this coincidence can point out that 2D electrons in such systems form the highly correlated viscous fluid.

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arXiv2023

Shear Bernstein modes in a two-dimensional electron liquid

Bernstein modes are formed as a result of non-local coupling of collective excitations and cyclotron harmonics in magnetized plasma. In degenerate solid state plasma they are typically associated with magnetoplasmons. A different type of Bernstein modes arises in two-dimensional electron liquid at sufficiently strong quasiparticle interaction. We consider Bernstein modes originating from coupling between quasiparticle cyclotron harmonics and shear magnetosound waves. The latter may be responsible for the giant peak in radio-frequency photoresistance observed in high-quality GaAs quantum wells. Using Landau-Silin kinetic equation with an arbitrary strength of the interparticle Landau interaction, we trace the reconstruction of Bernstein mode spectrum in high-quality 2D electron systems across the crossover between weakly interacting degenerate electron gas and the correlated electron liquid. Sensitivity of Bernstein modes to the strength of quasiparticle interaction allows one to use them for spectroscopy of Landau interaction function in the electron Fermi liquids.

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arXiv2023

Hydrodynamic magnetotransport in two-dimensional electron systems with macroscopic obstacles

In high-quality conductors, the hydrodynamic regime of electron transport has been recently realized. In this work we theoretically investigate magnetotransport of a viscous electron fluid in samples with electron-impermeable obstacles. We use the two approaches to describe the fluid flow. The first one is based on the equations of hydrodynamics of a charged fluid, which assume that the kinetic equation takes into account the two harmonics of the electron distribution function. The second approach is based on the equations that are obtained by taking into account three harmonics of the distribution function (''quasi-hydrodynamics''). Within the hydrodynamic approach, we consider the cases of the rough and the smooth edges of the disks, on which the electron scattering is diffusive or specular, respectively. The longitudinal magnetoresistivity turns out to be strong and negative, the same for both rough and smooth discs edges to within small corrections. For rough discs, the Hall resistivity is equal to its standard value. For smooth discs the Hall resistance acquire a small correction to the standard value, proportional to the Hall viscosity. In the quasi-hydrodynamic approach, we considered the case of smooth discs and small magnetic fields. In the regime when the flow is substantially different from the hydrodynamic one, the longitudinal resistivity does not depend on the shear stress relaxation time (but depends on the relaxation time of the third angular harmonic), while the correction to the standard Hall resistivity does not depend on both relaxation times. We compare the results of the hydrodynamic calculation of the longitudinal resistance with the experimental data on magnetotransport in high-quality GaAs quantum wells with macroscopic defects. A good agreement of theory and experiment evidences in favor of the realization of the hydrodynamic transport regime in such systems.

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arXiv2022

Hall effect in Poiseuille flow of two-dimensional electron fluid

The hydrodynamic regime of charge transport has been recently realized in high-quality conductors. In the hydrodynamic as well as in the Ohmic regimes the main part of the Hall resistance of a long sample is determined by the balance between the Lorentz force and the electric force, acting on conduction electrons. Experimentally observed deviations of the Hall resistance in hydrodynamic samples from such the ''standard'' value are usually associated with the Hall viscosity term in the Navier-Stokes equation. In this work we theoretically study the Hall effect in a Poiseuille flow of a two-dimensional electron fluid. We show that the near-edge semiballistic layers with the width of the order of the inter-particle mean free path, which inevitably appear near sample edges, give the contribution to the Hall resistance which is comparable with the bulk contribution from the Hall viscosity. In this way, the measured deviations of the Hall resistance from the ''standard'' one in hydrodynamic samples by the usual contact techniques should be associated with both the Hall viscosity in the bulk and the semiballistic effects in the near-edge layers

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arXiv2022

Rotational viscosity in spin resonance of hydrodynamic electrons

In novel ultra-pure materials electrons can form a viscous fluid, which is fundamentally different by its dynamics from the electron gas in ordinary conductors with significant density of defects. The shape of the non-stationary flow of such electron fluid is similar to the alternating flow of blood in large-radius arteries [J. R. Womersley, J. Physiol. 127, 552 (1955)]. The rotational viscosity effect is responsible for interconnection between the dynamics of electron spins and flow inhomogeneities. In particular, it induces the spin polarization of electrons in a curled flow via an internal spin-orbit torque acting on electron spins. Here we show that this effect in an electron fluid placed in a magnetic field leads to a correction to the ac sample impedance, which has a resonance at the Larmor frequency of electrons. In this way, via the electrically detected spin resonance the Womersley flow of an electron fluid can be visualized and the rotational viscosity can be measured.

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arXiv2022

Spin imaging of Poiseuille flow of viscous electronic fluid

Recent progress in fabricating high-quality conductors with small densities of defects has initiated the studies of the viscous electron fluid and has motivated the search for the evidences of the hydrodynamic regime of electron transport. In this work we come up with the spin imaging technique allowing us to attest to the emergence of electron hydrodynamic flows. Based on numerical calculations we demonstrate that the injected electron spin density is inhomogeneous across the channel when the viscous electron fluid forms the Poiseuille flow. We also argue that the Hanle curves at different positions across the channel acquire relative phase shifts resulting from the variation of the electron drift velocity in inhomogeneous hydrodynamic flows. The studied effects can be employed to evidence and study the viscous electron fluid non-invasively.

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arXiv2021

Ballistic flow of two-dimensional electrons in a magnetic field

In conductors with a very small density of defects, electrons at low temperatures collide predominantly with the edges of a sample. Therefore, the ballistic regime of charge and heat transport is realized. The application of a perpendicular magnetic field substantially modifies the character of ballistic transport. For the case of two-dimensional (2D) electrons in the magnetic fields corresponding to the diameter of the cyclotron trajectories smaller than the sample width a hydrodynamic transport regime is formed. In the latter regime, the flow is mainly controlled by rare electron-electron collisions, which determine the viscosity effect. In this work, we study the ballistic flow of 2D electrons in long samples in magnetic fields up to the critical field of the transition to the hydrodynamic regime. From the solution of the kinetic equation, we obtain analytical formulas for the profiles of the current density and the Hall electric field far and near the ballistic-hydrodynamic transition as well as for the longitudinal and the Hall resistances in these ranges. Our theoretical results, apparently, describe the observed longitudinal resistance of pure graphene samples in the diapason of magnetic fields below the ballistic-hydrodynamic transition.

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arXiv2021

Ballistic-hydrodynamic phase transition in flow of two-dimensional electrons

Phase transitions are characterized by a sharp change in the type of dynamics of microparticles, and their description usually requires quantum mechanics. Recently, a peculiar type of conductors was discovered in which two-dimensional (2D) electrons form a viscous fluid. In this work we reveal that such electron fluid in high-quality samples can be formed from ballistic electrons via a phase transition. For this purpose, we theoretically study the evolution of a ballistic flow of 2D weakly interacting electrons with an increase of magnetic field and trace an emergence of a fluid fraction at a certain critical field. Such restructuring of the flow manifests itself in a kink in magnetic-field dependencies of the longitudinal and the Hall resistances. It is remarkable that the studied phase transition has a classical-mechanical origin and is determined by both the ballistic size effects and the electron-electron scattering. Our analysis shows that this effect was apparently observed in the recent transport experiments on 2D electrons in graphene and high-mobility GaAs quantum wells.

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arXiv2021

Anisotropic magnetoresistance and memory effect in bulk systems with extended defects

Memory effects can have a profound impact on the resistivity of semiconductor systems, resulting in giant negative magnetoresistance and MIRO phenomena. This work opens the discussion of the memory effects in 3D conducting systems featured by the presence of the extended one-dimensional defects, such as screw dislocations or static charge stripes. We demonstrate that accounting for the memory effect, that is the capture of electrons on collisionless spiral trajectories winding around extended defects, leads to the strong negative magnetoresistance in case when the external magnetic field direction becomes parallel to the defects axis. This effect gives rise to a significant magnetoresistance anisotropy already for an isotropic Fermi surface and no spin-orbit effects. The proposed resistivity feature can be used to detect one-dimensional scattering defects in these systems.

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arXiv2021

Electron density effect on spin-orbit interaction in [001] GaAs quantum wells

The spin-orbit interaction of two-dimensional (2D) electrons in semiconductor quantum wells is usually considered to be determined by the band profile of a heterostructure. In the GaAs/AlGaAs type heterosystems, this interaction consists of the isotropic Bychkov-Rashba term, which is absent in symmetric wells, and the anisotropic Dresselhaus term, reflecting the lattice symmetry. It is well-known that the first term can be controlled by electric fields in the growth direction: external or internal, induced by a charge density of 2D electrons. In this work we reveal that the 2D electron charge can substantially affect also the Dresselhaus interaction in symmetric quantum wells. Within the one-band electron Hamiltonian containing, together with the bulk Dresselhaus interaction, the two contributions to the Dresselhaus term from the quantum well interfaces, we show that the internal electric field from the 2D electron charge density can substantially renormalize the anisotropic spin-orbit interaction of 2D electrons. This effect may be important in quantitative studies of spin-dependent phenomena in quantum wells.

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arXiv2020

Viscosity of two-dimensional electrons

The hydrodynamic regime of electron transport has been recently realized in conductors with ultra-low densities of defects. Although relaxation processes in two-dimensional (2D) fluids have been studied in many theoretical works, the viscosity of the realistic Fermi gas of 2D electrons having the quadratic energy spectrum and interacting by Coulomb's law has not been reliably determined either in theory or in experiment up to now. Here we construct a theory of viscosity and thermal conductivity in such system. We compare the calculated viscosity of the 2D electron Fermi gas and the previously known viscosity of a 2D Fermi liquid with available experimental data extracted from the hydrodynamic negative magnetoresistance of the best-quality GaAs quantum wells. Based on this comparison, we argue that measurements of the temperature dependence of the viscosity can allow to trace the transition between an electron Fermi liquid and a Fermi gas.

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arXiv2019

The Hall effect in ballistic flow of two-dimensional interacting particles

In high-quality solid-state systems at low temperatures, the hydrodynamic or the ballistic regimes of heat and charge transport are realized in the electron and the phonon systems. In these regimes, the thermal and the electric conductance of the sample can reach abnormally large magnitudes. In this paper, we study the Hall effect in a system of interacting two-dimensional charged particles in a ballistic regime. We demonstrated that the Hall electric field is caused by a change in the densities of particles due to the effect of external fields on their free motions between the sample edges. In one-component (electron or hole) systems the Hall coefficient turns out to one half compared with the one in conventional disordered Ohmic samples. This result is consistent with the recent experiment on measuring of the Hall resistance in ultra-high-mobility GaAs quantum wells. In two-component electron-hole systems the Hall electric field depends linearly on the difference between the concentrations of electrons and holes near the charge neutrality point (the equilibrium electron and hole densities coincide) and saturates to the Hall field of a one-component system far from the charge neutrality point. We also studied the corrections to magnetoresistance and the Hall electric field due to inter-particle scattering being a precursor of forming a viscous flow. For the samples shorter than the inter-particle scattering length, the obtained corrections govern the dependencies of magnetoresistance and the Hall field on temperature.

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