arXiv subjects

A. K. Bakarov

Publications and source records attributed to A. K. Bakarov.

At least 19 recordsLinked to original sources

arXiv2026

Corbino-Enhanced Supersonic Acoustic-Emission Threshold in a GaAs Two-Dimensional Electron System

We report nonlinear differential-resistance measurements in a high-mobility GaAs/AlGaAs two-dimensional electron system patterned in a Corbino geometry. At zero magnetic field, $R_{\mathrm{diff}}(I_{dc})$ exhibits a pronounced polarity-selective threshold peak on the negative-current branch, gradually suppressed by a perpendicular magnetic field. We interpret the Corbino anomaly as a local Cherenkov-like threshold for acoustic phonon emission, enabled by the radial current concentration $j_r(r)=I/(2πr)$, which drives the local electron velocity above the sound velocity in a region adjacent to the inner contact. The polarity selectivity is attributed to Peltier heating and cooling, which modify the local thermal and boundary conditions near the contact, rather than to the kinematic threshold itself. Our results identify the Corbino geometry as a sensitive platform for probing local nonequilibrium electron--phonon processes in a high-mobility electron system within an independently established hydrodynamic-crossover regime and suggest that the inner Corbino contact can act as a geometry-defined source for supersonic acoustic emission.

cond-mat.mes-hall↗

arXiv2026

Hydrodynamic magnetotransport in a GaAs Corbino geometry

We report the observation of positive magnetoresistance in high-mobility GaAs Corbino devices. Over a broad intermediate-temperature range, the resistance exhibits a quadratic dependence on perpendicular magnetic field. We analyze the data within hydrodynamic theories of magnetotransport in the Corbino geometry, which describe the crossover between the diffusive and viscous regimes, including finite-slip boundary conditions appropriate for current-penetrable contacts. The extracted relaxation rates are consistent with an approximately $T^2$ temperature dependence of the electron-electron scattering contribution. The extracted viscous relaxation parameters are consistent with those obtained from Hall-bar measurements. Comparison with theory indicates that the observed magnetoresistance is predominantly governed by the bulk hydrodynamic response, while finite slip modifies the Stokes--Ohm crossover quantitatively and the field-dependent boundary voltage provides a separate correction. These results show that Corbino magnetotransport can serve as a complementary bulk-sensitive probe of viscous electron flow.

cond-mat.mes-hall↗

arXiv2026

Electron Hydrodynamics and Bernoulli Effect in Venturi-Shaped 2D Systems

The study of electron hydrodynamics provides a powerful framework for understanding transport in ultraclean conductors, yet experimental evidence has thus far been largely restricted to the linear-response regime. Here, we report the direct observation of a strongly nonlinear transport regime in a high-mobility two-dimensional electron system. By engineering devices with a Venturi-shaped wedge geometry specifically designed to enhance convective nonlinearities, we uncover a pronounced nonlinear voltage response and large diodicity in the current-voltage characteristics. Our experimental findings show quantitative agreement with a theoretical model that attributes the observed nonlinearity to the convective acceleration of the electron fluid, analogous to the Bernoulli effect. These results provide compelling evidence for the applicability of the hydrodynamic framework to two-dimensional electron transport and open new avenues for exploring nonlinear and preturbulent phenomena in solid-state systems.

cond-mat.mes-hall↗

arXiv2026

Magnetophonon Resistance Oscillations in Structures with a GaAs Quantum Well and Barriers of AlAs/GaAs$\langleδ$-Si$\rangle$ Superlattices

Magnetophonon resistance oscillations (MPR) associated with the resonant scattering of electrons by optical phonons at temperatures of 77-240 K, as well as resonant scattering of electrons by acoustic phonons (PIRO) at temperatures of 10-25 K, were investigated in the same samples featuring a GaAs quantum well and AlAs/GaAs superlattice barriers doped with Si. The study of MPR demonstrated that resonant electron scattering occurs on bulk longitudinal optical phonons and does not depend on the dimensionality of the system or inter-subband transitions in systems with two subbands of size quantization. However, the amplitude of the oscillation with number $N=1$ in two-dimensional structures depends on the interplay of scattering mechanisms, which, in turn, is influenced by the structure of the system. As for PIRO, in samples with two size quantization subbands, resonant electron scattering by longitudinal acoustic phonons is observed against the background of inter-subband transitions (MISO), leading to their interference.

cond-mat.mes-hall↗

arXiv2026

Effect of electric current on optical response of viscous electron-hole plasma

The influence of the Hall voltage on the photoluminescence of a dense hydrodynamic electron-hole plasma laser generated in a mesoscopic n-doped GaAs channel under intense laser excitation is studied. Laser excitation induces an interband current determined by the recombination of photogenerated electron-hole pairs. As a result, background electrons drifting under the influence of the Hall voltage form an effective Hall current. The Coulomb drag caused by the Hall current causes the accumulation of light holes, leading to the appearance of a double photoluminescence line formed by the recombination of excitons and trions. In contrast, in the absence of a Hall current, the shift in the photoluminescence energy associated with heavy holes occurs due to the electric field created by the Hall potential difference.

cond-mat.mes-hall↗

arXiv2026

Spectroscopy of Heat Transport and Violation of the Wiedemann--Franz Law in a GaAs Hydrodynamic Mesoscopic Channel

The Wiedemann--Franz law, which determines the universality of the ratio of thermal conductivity to electrical conductivity, is studied in the hydrodynamic electron transport regime, where electron--electron scattering predominates over scattering by disorder. In this case, the different relaxation of electric and thermal currents can lead to a violation of the Wiedemann--Franz law, which is expected to be even more pronounced in mesoscopic electron systems. This paper reports the propagation of hot electrons in a GaAs hydrodynamic narrow channel, studied using micrometer-resolution photoluminescence thermometry. A temperature dependence of the Lorenz number was obtained, indicating a violation of the Wiedemann--Franz law. The important role of narrow constrictions in this violation was also demonstrated, and theoretical arguments are presented.

cond-mat.mes-hall↗

arXiv2026

Viscous Electron Flow and Nonlinear Magnetotransport in 2D Channels

We examine nonlinear transport in a viscous two-dimensional electron fluid within narrow GaAs channels. The differential magnetoresistance shows nonmonotonic behavior, a signature of electron pairing in the hydrodynamic regime. Theoretical models that account for both the influence of these interactions on shear stress relaxation and viscosity changes from electron heating show good agreement with the data. The nonlinear regime thus reveals how such correlated states govern the hydrodynamic behavior of the electron fluid. Our findings establish the nonlinear transport regime as a powerful probe for dissecting the complex interplay of correlated electron states and momentum relaxation in the hydrodynamic flow of an electron fluid.

cond-mat.mes-hall↗

arXiv2026

Giant Shubnikov-de Haas Oscillations with V-Shaped Minima in a High-Mobility Two-Dimensional Electron Gas: Experiment and Phenomenological Model

Giant Shubnikov-de Haas oscillations (SdHO) with V-shaped minima are experimentally studied in a high-mobility two-dimensional electron gas based on GaAs/AlGaAs heterostructures. A phenomenological model with two parameters (transport momentum relaxation time $τ_{\text{tr}}$ and quantum scattering time $τ_q$) is developed, accurately describing experimentally measured magnetoresistance over an unexpectedly wide range of magnetic fields (up to 3.5 T) and temperatures (from 2 K to 15 K). The model combines: (i) a quasiclassical density of states with a magnetic-field-dependent Gaussian broadening of Landau levels, (ii) a momentum relaxation time scaling with the density of states, and (iii) oscillations of the Fermi level at a fixed electron density. This model reproduces V-shaped oscillation minima with zero-resistance points, a smooth background of positive magnetoresistance, and enables the extraction of $τ_q$ and $τ_{\text{tr}}$ even in microstructures where ballistic and viscous effects dominate at low fields. As expected, the temperature dependence reveals that $τ_{\text{tr}}$ scales inversely with temperature due to acoustic phonon scattering, while $τ_q$ remains temperature-independent.

cond-mat.mes-hall↗

arXiv2025

Current-induced Magnetoexcitons in Mesoscopic Electron-hole Plasma

A radical restructuring of the optical response of highly excited electron-hole plasma formed in a mesoscopic GaAs/AlGaAs channel in a quantizing magnetic field when an electric current flows in the channel has been discovered. In the absence of current, the emission spectra are caused by transitions between Landau levels formed in the conduction band and in the valence band of heavy holes. A critical electric current leads to a drastic change in the emission spectra with a predominant contribution from light holes. It is shown that the current causes local accumulation of light holes due to Coulomb drag, which leads to strong electron-hole coupling and, as a consequence, the formation of excitons and trions.

cond-mat.mes-hall↗

arXiv2025

Obstacle-Induced Gurzhi Effect and Hydrodynamic Electron Flow in Two-Dimensional Systems

The viscous flow of electrons in a narrow channel requires both strong electron-electron interactions and no-slip boundary conditions. However, introducing obstacles within the liquid can significantly increase flow resistance and, as a result, amplify the effects of viscosity. Even in samples with smooth walls, the presence of an obstacle can strongly alter electron behavior, leading to pronounced hydrodynamic effects. We investigated transport in mesoscopic samples containing a disordered array of obstacles. In contrast to samples without obstacles, which do not show a decrease in resistivity with rising temperature, samples with obstacles exhibit a significant resistivity reduction as temperature increases (the Gurzhi effect). By measuring the negative magnetoresistance, we extracted shear viscosity and other parameters through comparison with theoretical predictions. Consequently, narrow-channel samples with a disordered obstacle array provide a valuable platform for studying hydrodynamic electron flow independently of boundary conditions.

cond-mat.mes-hall↗

arXiv2024

Bulk and shear viscosities in multicomponent 2D electron system

We investigated magnetotransport in mesoscopic samples containing electrons from three different subbands in GaAs triple wells. At high temperatures, we observed positive magnetoresistance, which we attribute to the imbalance between different types of particles that are sensitive to bulk viscosities. At low temperatures, we found negative magnetoresistance, attributed to shear viscosity. By analyzing the magnetoresistance data, we were able to determine both viscosities. Remarkably, the electronic bulk viscosity was significantly larger than the shear viscosity. Studying multicomponent electron systems in the hydrodynamic regime presents an intriguing opportunity to further explore the physics in systems with high bulk viscosity.

cond-mat.mes-hall↗

arXiv2024

Hydrodynamics of electron-hole fluid photogenerated in a mesoscopic two-dimensional channel

The dynamics of the diffusion flow of holes photoinjected into a mesoscopic GaAs channel of variable width, where they, together with background electrons, form a hydrodynamic electron-hole fluid, is studied using time-resolved microphotoluminescence. It is found that the rate of recombination of photoinjected holes, which is proportional to the rate of their flow, decreases when holes pass through the expanded sections of the channel. In fact, this is the Venturi effect, which consists in a decrease in the velocity of the fluid in the expanded sections of the pipe. Moreover, a non-uniform diffusion velocity profile is observed, similar to the parabolic Hagen-Poiseuille velocity profile, which indicates a viscous hydrodynamic flow. It is shown that in argeement with a theory, the magnetic field strongly suppresses the viscosity of the electron-hole fluid. Additional evidence of the viscous nature of the studied electron-hole fluid is the observed increase in the recombination rate with increasing temperature, which is similar to the decrease in the electrical resistance of viscous electrons with temperature.

cond-mat.mes-hall↗

arXiv2024

Optical realization of magneto-intersubband oscillations

We report on the optical realization of the magneto-intersubband oscillations that have been measured in the sub-terahertz transmittance of a GaAs quantum well with two subbands occupied. Following their dc analogue, the oscillations are periodic in the inverse magnetic field with the period governed by the subband gap. Their magnitude and polarization dependence accurately follow the presented simplified version of the dynamic magneto-intersubband oscillations equation that naturally combines dc magneto-intersabband oscillations with microwave-induced resistance oscillations (MIRO). Simultaneously measured photoresistance also reveals its strong sensitivity to the sign of the circular polarization, proving the used theoretical modeling.

cond-mat.mes-hall↗

arXiv2023

Geometric engineering of viscous magnetotransport in a two-dimensional electron system

In this study, we present our experimental investigation on the magnetotransport properties of a two-dimensional electron system in GaAs quantum wells utilizing a variety of device geometries, including obstacles with thin barriers and periodic width variations. Our primary focus is to explore the impact of these geometries on the electron viscous flow parameters, enabling precise manipulation of hydrodynamic effects under controlled conditions. Through an analysis of the large negative magnetoresistivity and zero field resistivity, we deduce the scattering times for electron-electron and electron-phonon interactions, as well as the effective channel width. Our findings confirm that the system under investigation serves as a tunable experimental platform for investigating hydrodynamic transport regimes at temperatures above 10 K.

cond-mat.mes-hall↗

arXiv2023

Influence of illumination on the quantum lifetime in selectively doped single GaAs quantum wells with short-period AlAs/GaAs superlattice barriers

The influence of illumination on a high mobility two-dimensional electron gas with high concentration of charge carriers is studied in selectively doped single GaAs quantum wells with short-period AlAs/GaAs superlattice barriers at a temperature T = 4.2 K in magnetic fields B < 2 T. It is shown that illumination at low temperatures in the studied heterostructures leads to an increase in the concentration, mobility, and quantum lifetime of electrons. An increase in the quantum lifetime due to illumination of single GaAs quantum wells with modulated superlattice doping is explained by a decrease in the effective concentration of remote ionized donors.

cond-mat.mes-hall↗

arXiv2022

Diffusion of photo-excited holes in viscous electron fluid

The diffusion of photo-generated holes is studied in a high-mobility mesoscopic GaAs\ channel where electrons exhibit hydrodynamic properties. It is shown that the injection of holes into such an electron system leads to the formation of a hydrodynamic three-component mixture consisted of electrons and photo-generated heavy and light holes. The obtained results are analyzed within the framework of ambipolar diffusion, which reveals characteristics of a viscous flow. Both hole types exhibit similar hydrodynamic characteristics. In such a way the diffusion lengths, ambipolar diffusion coefficient and the effective viscosity of the electron-hole system are determined.

cond-mat.mes-hall↗

arXiv2021

Temperature Damping of Magneto-Intersubband Resistance Oscillations in Magnetically Entangled Subbands

Magneto-intersubband resistance oscillations (MISO) of highly mobile 2D electrons in symmetric GaAs quantum wells with two populated subbands are studied in magnetic fields tilted from the normal to the 2D electron layer at different temperatures $T$. Decrease of MISO amplitude with temperature increase is observed. At moderate tilts the temperature decrease of MISO amplitude is consistent with decrease of Dingle factor due to reduction of quantum electron lifetime at high temperatures. At large tilts new regime of strong MISO suppression with the temperature is observed. Proposed model relates this suppression to magnetic entanglement between subbands, leading to beating in oscillating density of states. The model yields corresponding temperature damping factor: $A_{MISO}(T)=X/\sinh(X)$, where $X=2π^2kTδf$ and $δf$ is difference frequency of oscillations of density of states in two subbands. This factor is in agreement with experiment. Fermi liquid enhancement of MISO amplitude is observed.

cond-mat.mes-hall↗

arXiv2021

Viscous magnetotransport and Gurzhi effect in bilayer electron system

We observe a large negative magnetoresistance and a decrease of resistivity with increasing temperature, known as the Gurzhi effect, in a bilayer electron (BL) system formed by a wide GaAs quantum well. A hydrodynamic model for the single fluid transport parameters in narrow channels is employed and successfully describes our experimental findings. We find that the electron-electron scattering in the bilayer is more intensive in comparison with a single-band well (SW). The hydrodynamic assumption implies a strong dependence on boundary conditions, which can be characterized by slip length, describing the behavior of a liquid near the edge. Our results reveal that slip length in a BL is shorter than in a SW, and that the BL system goes deeper into the hydrodynamic regime. This is in agreement with the model proposed where the slip length is of the order of the electron-electron mean free path.

cond-mat.mes-hall↗