arXiv subjects

M. V. Entin

Publications and source records attributed to M. V. Entin.

At least 19 recordsLinked to original sources

arXiv2026

Theory of transmittance of narrow quantum wires intersection in 2D systems

Two-dimensional nanosystems the characteristic sizes of which are less than the quasiparticle wavelength have been studied. This parameter allows replacement of the Shr\"odinger equation by the Laplace one. The latter permits us exact solution using the conformal mapping technique. Bulged 1D quantum wires based on 2D system are considered. The electron states in these systems have been studied. The transmittance of the intersection between the narrow quantum strips has been studied. It is assumed that strip widths are less than the electron wavelength, so that they are the tunnel conductors. The transmittances of T-like and X-like wire crossings have been found.

cond-mat.mes-hall↗

arXiv2025

Resistivity of non-Galilean invariant two dimensional Dirac system

We revisited the influence of electron-electron scattering on the resistivity of a two-dimensional system with linear spectrum. In conventional systems with parabolic spectrum, where Umklapp scattering is either prohibited or ineffective due to small Fermi surface, particle-particle scattering does not contribute to conductivity because it does not change the total momentum. However, within the framework of Boltzmann kinetic model, we demonstrate that electron-electron scattering in Dirac systems can significantly contribute to conductivity, producing distinct temperature-dependent corrections: a T\textsuperscript{4} behavior at low temperatures and T\textsuperscript{2} dependence at moderate temperatures. While the predicted T\textsuperscript{4} scaling is not observed experimentally -- likely suppressed by dominant weak localization effects -- the T\textsuperscript{2} scaling is clearly confirmed in our measurements. Specifically, temperature-dependent resistivity data from gapless single-valley HgTe quantum well exhibit T\textsuperscript{2} corrections, which align well with theoretical predictions. Thus, we challenge the paradigm that T\textsuperscript{2} term in resistivity is absent in single-band 2D metals.

cond-mat.mes-hall↗

arXiv2024

Interaction-controlled transport in a two-dimensional massless-massive Dirac system: Transition from degenerate to nondegenerate regimes

The resistivity of two-dimensional (2D) metals generally exhibits insensitivity to electron-electron scattering. However, it's worth noting that Galilean invariance may not hold true in systems characterized by a spectrum containing multiple electronic branches or in scenarios involving electron-hole plasma. In the context of our study, we focus on 2D electrons confined within a triple quantum well (TQW) based on HgTe. This system displays a coexistence of energy bands featuring both linear and parabolic-like spectra at low energy and, therefore, lacks the Galilean invariance. This research employs a combined theoretical and experimental approach to investigate the transport properties of this two-component system across various regimes. By manipulating carrier density and temperature, we tune our system from a fully degenerate regime, where resistance follows a temperature-dependent behavior proportional to $T^2$, to a regime where both types of electrons adhere to Boltzmann statistics. In the non-degenerate regime, electron interactions lead to resistance that is weakly dependent on temperature. Notably, our experimental observations closely align with the theoretical predictions derived in this study. This work establishes the HgTe-based TQW as a promising platform for exploring different interaction dominant scenarios for the massless-massive Dirac system.9 pages, 8 figures

cond-mat.mes-hall↗

arXiv2024

Electron-hole scattering-induced temperature behaviour of HgTe-based semimetal quantum well

The semimetal quantum well (QW) based on HgTe structures exhibiting unusual transport properties at low temperature is examined experimentally. It demonstrates either a linear or quadratic growth of resistance with temperature at different top-gate voltages in the semimetal regime. We develop a theoretical model of HgTe-based semimetal QW resistance temperature dependence based on electron-hole scattering processes at low temperatures. We apply the Boltzmann transport equation approach to study the effect of electron-hole scattering in a semimetal QW. The calculated temperature behavior of 2D semimetal resistivity demonstrates an excellent agreement with experimental findings.

cond-mat.mes-hall↗

arXiv2024

Interaction dominated transport in 2D conductors: from degenerate to partially-degenerate regime

In this study, we investigate the conductivity of a two-dimensional (2D) system in HgTe quantum well comprising two types of carriers with linear and quadratic spectra, respectively. The interactions between the two-dimensional Dirac holes and the heavy holes lead to the breakdown of Galilean invariance, resulting in interaction-limited resistivity. Our exploration of the transport properties spans from low temperatures, where both subsystems are fully degenerate, to higher temperatures, where the Dirac holes remain degenerate while the heavy holes follow Boltzmann statistics, creating a partially degenerate regime. Through a developed theory, we successfully predict the behavior of resistivity as $ρ\sim T^2$ and $ρ\sim T^{3}$ for the fully degenerate and partially degenerate regimes, respectively, which is in reasonable agreement with experimental observations. Notably, at elevated temperatures, the interaction-limited resistivity surpasses the resistivity caused by impurity scattering by a factor of 5-6. These findings imply that the investigated system serves as a versatile experimental platform for exploring various interaction-limited transport regimes in two component plasma.

cond-mat.mes-hall↗

arXiv2023

Orbital momentum excitation by interband optical transitions in a 2D system illuminated by twisted light

Illumination of a two-dimensional system by a twisted light beam is considered in order to find specific effects caused by twisting. Direct interband transitions between the valence and conduction bands are supposed. The generation rates of the electron orbital momentum is found. A kinetic equation for an orbital momentum distribution function is formulated and solved. The mean electron orbital momentum is found.

cond-mat.mes-hall↗

arXiv2022

Spin structure and spin magnetic susceptibility of two-dimensional Wigner clusters

Spin states of two-dimensional Wigner clusters are considered at low temperatures, when all electrons are in ground coordinate states. The spin subsystem behavior is determined by antiferromagnetic exchange integrals. The spin states in such a system in the presence of a magnetic field are described in terms of the Ising model. The spin structure, correlation function, and magnetic susceptibility of the cluster are found by computer simulations. It is shown that the spin susceptibility experiences oscillations with respect to the magnetic field, owing to the magnetoinduced spin subsystem rearrangements.

cond-mat.mes-hall↗

arXiv2022

Electron diffusion induced valley Hall effect and nonlinear galvanodiffusive transport in hexagonal 2D Dirac monolayer materials

Diffusion currents are theoretically examined in two-dimensional Dirac materials, such as those of the transition metal dichalcogenides (TMD) family. The transversal effects are analogues of the valley Hall (VHE) and photogalvanic (PGE) transport phenomena in case when the electron driving force is not an electric field but a gradient of electron density distribution in the sample. The latter can be created by a finite-sized laser spot or by the injection of electrons from other materials. We develop the theory of diffusive VHE effect assuming the anisotropic electron-short-range-impurity skew scattering. The electron PGE-like transport caused by higher electron-density derivatives is analyzed assuming the trigonal warping anisotropy of electron valleys in a TMD monolayer. The nonlinear responses on electron-density gradient are studied as well. The isotropic processes of electron scattering off the short-range and Coulomb centers are taken into account in the PGE-like transport theory.

cond-mat.mes-hall↗

arXiv2021

Transport through the network of topological channels in HgTe based quantum well

Topological insulators represent a new quantum state of matter which is characterized by edge or surface states and an insulating band gap in the bulk. In a two dimensional (2D) system based on the HgTe quantum well (QW) of critical width random deviations of the well width from its average value result in local crossovers from zero gap 2D Dirac fermion system to either the 2D topological insulator or the ordinary insulator, forming a complicated in-plane network of helical channels along the zero-gap lines. We have studied experimentally the transport properties of the critical width HgTe quantum wells near the Dirac point, where the conductance is determined by a percolation along the zero-gap lines. The experimental results confirm the presence of percolating conducting channels of a finite width. Our work establishes the critical width HgTe QW as a promising platform for the study of the interplay between topology and localization.

cond-mat.mes-hall↗

arXiv2021

Nonlinear circular valley photogalvanic effect

We develop a theory of circular photogalvanic effect in non-gyrotropic two-dimensional transition metal dichalcogenide monolayers under interband optical transitions. Oblique incidence of circularly-polarized electromagnetic field or normal incidence of elliptically polarized electromagnetic field is assumed. In contrast to the linear-in-intensity conventional photogalvanic effect, the effect considered here arises in the second intensity order. The effect is conditioned by i) the predominant population of the valleys by the circular in-plane electromagnetic field component and ii) the direct drift of the photo-excited carriers by the linear-polarized in-plane electromagnetic field component in the presence of trigonal valley asymmetry.

cond-mat.mes-hall↗

arXiv2021

Theory of electron states in a twisted two-valley 2D system

A system similar to gapped graphene (for example, fluorinated) containing two or more electron valleys is considered. It is assumed that the material has a sector cut and is deformed in the plane and the the cut edges are connected to form an adiabatically curved atomic net without extended defects. We neglect the deformation potential. In such a system, the local momentum of the valley center ${\bf K}$ acts as the vector potential of fictitious magnetic field. We found the electron states in such system in the case of orientation ${\bf K}$ along the azimuth of geometric space at any point. It is shown that the vector potential results in the appearance of local discrete electron states. Mathematically, the problem is mapped onto the Coulomb problem with an effective charge depending on ${\bf K}$.

cond-mat.mes-hall↗

arXiv2021

Electron states on the smooth edge of 2D topological insulator: elastic backscattering and light absorption

The 2D TI edge states are considered within the Volkov-Pankratov (VP) Hamiltonian. A smooth transition between TI and OI is assumed. The edge states are formed in the total gap of homogeneous 2D material. A pair of these states are of linear dispersion, others have gapped Dirac spectra. The optical selection rules are found. The optical transitions between the neighboring edge states appear in the global 2D gap for the in-plane light electric field directed across the edge. The electrons in linear edge states have no backscattering, that is indicative of the fact of topological protection. However, when linear edge states get to the energy domain of Dirac edge states, the backscattering becomes permitted. The elastic backscattering rate is found. The Drude-like conductivity is found when the Fermi level gets into the energy domain of the coexistence of linear and Dirac edge states. The localization edge conductance of a finite sample at zero temperature is determined.

cond-mat.mes-hall↗

arXiv2021

Magnetoresistance of edge states of a two-dimensional topological insulator

The theory of magnetoresistance of the edge state of a two-dimensional topological insulator is developed. The magnetic field violates the time-reversal invariance. Magnetoresistance arises due to the energy gap opened by a magnetic field parallel to the sample surface. The combined action of impurities and the magnetic field causes backscattering of edge electrons. Although impurities are necessary for scattering, sufficiently strong interaction with impurities leads to the suppression of backscattering.

cond-mat.mes-hall↗

arXiv2020

Conductivity of a two-dimensional HgTe layer near the critical width: The role of developed edge states network and random mixture of $p$- and $n$-domains

The conductivity of a two-dimensional HgTe quantum well with a width $\sim$6.3~nm, close to the transition from ordinary to topological insulating phases, is studied. The Fermi level is supposed to get to the overall energy gap. The consideration is based on the percolation theory. We have found that the width fluctuations convert the system to a random mixture of domains with positive and negative energy gaps with internal edge states formed near zero gap lines. In the case with no potential fluctuations, the conductance of a finite sample is provided by a random edge states network. The zero-temperature conductivity of an infinite sample is determined by the free motion of electrons along the zero-gap lines and tunneling between them. The conductance of a single $p$-$n$ junction, which is crossed by the edge state, is found. The result is applied to the situation when potential fluctuations transform the system to a mixture of $p$- and $n$-domains. It is stated that the tunneling across $p$-$n$ junctions forbids the low-temperature conductivity of a random system, but the latter is restored due to the random edge states crossing the junctions.

cond-mat.mes-hall↗

arXiv2019

Scattering of Electrons between Edge and Two-Dimensional States of a Two-Dimensional Topological Insulator and the Conductivity of the Topological Insulator Strip in a Metallic State

The lifetime of electrons on edge states of a two-dimensional topological insulator against the background of an allowed two-dimensional band has been determined. It has been shown that this time in the case of scattering on Coulomb impurities can be significantly larger than the mean free time of two-dimensional electrons. As a result, the conductivity of the metallic two-dimensional topological insulator strip can be determined primarily by edge states.

cond-mat.mes-hall↗

arXiv2018

Thermopower of a Two-Dimensional Semimetal in a HgTe Quantum Well

The thermopower in a two-dimensional semimetal existing in HgTe quantum wells 18-21 nm thick has been studied experimentally and theoretically for the first time. It has been found theoretically and experimentally that the thermopower has two components - diffusion and phonon drag and that the second component is several times larger than the first. It has been concluded that the electron-hole scattering plays an important role in both mechanisms of the thermopower.

cond-mat.mes-hall↗

arXiv2018

Microwave absorption in a 2D topological insulators with a developed network of edge states

The 2D HgTe quantum well is analyzed based on the assumption that the width fluctuations convert the system to a random mixture of domains with positive and negative energy gaps. The borders between ordinary and topological insulator phases form a network of the edge states covering the overall sample. The optical transitions within the edge states yield the 2D absorption. The qualitative consideration is based on the model of optical intraedge transitions in curved edge states together with the percolation arguments.

cond-mat.mes-hall↗

arXiv2018

Photogalvanic Effect in 2D Dichalcogenides Under Double Illumination

We study the photogalvanic effect caused by a simultaneous action of circular-polarized interband and linearly-polarized intraband illuminations. It is found that, in such conditions, the steady photocurrent appears. The effect originates from the valley-selective pumping by the circular light, the trigonal asymmetry of the valleys together with the even asymmetry of the linearly-polarized light, that produces a polar in-plane asymmetry of the electron and hole distribution functions, leading to the photocurrent. The approach is based on the solution of the classical kinetic equation for carriers with accounting for the quantum interband excitation.

cond-mat.mes-hall↗