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Recently, a hydrodynamic behavior of ultrahigh mobility viscous two-dimensional electron gas in GaAs/AlGaAs quantum well was intensively studied based on relevant negative magnetoresistance (NMR) data. The two-dimensional Gurzhi model with(without) simplification combined with extra assumptions on electron-electron collisions rate often lead to a certain agreement with experiment. We provide ab initio analysis of the NMR data[Q. Shi et al, Phys. Rev. B. 89, 201301(R) (2014)] and demonstrate exceptional agreement with the uncut Gurzhi model attracting a single fitting parameter of the effective stream width. Our approach allows one to identify the intrinsic carrier mobility higher than that deduced by conventional methods. The NMR data analysis is proposed for powerful tool for two-dimensional viscometry., Comment: 4 pages, 4 figures, minor changes

The main results of the commented article do not raise objections, but their final processing seems doubtful. Namely, the spectra of zero-field plasmon with a fixed angular momentum $l = 0.1..4$ was scaled using a certain reference frequency and, then displayed as a function of a specific screening parameter. Oddly enough, it turned out that the reference frequency includes the screening parameter explicitly. Obviously, it is a trivial error in scaling procedure. For this reason the physical meaning of the result becomes lost, especially for zero value of screening parameter. The similar scaling method was performed for magnetoplasmon spectra at fixed values $0;0.5;\infty$ of screening parameter. Again, the case of zero screening parameter is doubtful. Both examples are exactly the source of misunderstandings. The original data for the axisymmetric plasmon $l=0$ were corrected and, then compared with the that followed from so-called telegraph line model, showing a difference of only 5 percent. We claim that the telegraph line model would be useful for describing disk-shaped plasmon devices with/without ring gratings., Comment: 1.5 pages, 1 figure

We investigate the dark axisymmetric plasmon spectrum for partially gated two-dimensional gas of the disk shape. The extension of the central gate spot provides a change in plasmon dispersion from the root to a linear dependence on the wave vector. Intriguingly, the interaction between neighboring modes occurs because of stepwise change in carrier screening across the circumference of the gate. This behavior is unexpected when changing from a fully screened to unscreened two-dimensional gas by increasing the dielectric width under the gate [A.L.Fetter, Phys.Rev.B 33, 5221 (1986)]. Our results provide the accurate identification of axisymmetric plasmon modes recently observed in experiment and, in addition, pave the way for feedback plasmon resonator study., Comment: 5 pages, 2 figures, bugs fixed

We propose the turnable THz generator built on two-dimensional analog of conventional Helmholtz resonator. The generator excitation is provided by current flow similar to whistle in conventional hydrodynamics. The output frequency, hydrodynamic parameters and practical realization of THz-whistle are discussed regarding the possible applications., Comment: 4/4

The highly disordered metals dropped into Ioffe-Regel transport regime at low temperatures match unexpectedly the hydrodynamic criteria of the shortest length scale entered the kinematic viscosity. Numerous hydrodynamic phenomena, therefore, could be of reality in this case., Comment: 2 pages, minor changes to v1

The longitudinal current in a three-dimensional conductor is accompanied by transverse magnetic field in a specimen bulk. The absence of the transverse current in a sample bulk requires a nonzero Hall electric field in transverse cross-section which provides the Lorentz force cancelation. The longitudinal current itself can be viewed as a collective drift of carriers in crossed magnetic and electric(Hall) fields. At low temperatures the enhanced carrier viscosity leads to nonuniform current flow whose transverse profile is sensitive to presence of $collinear$ diamagnetic currents at the sample inner walls. Former dissipative the longitudinal current becomes purely diamagnetic at certain critical temperature. The superconductivity sets on. The current and transverse magnetic field become pushed out from the sample bulk towards the inner wall. Magnetic properties of a sample resemble those expected for ideal diamagnet. The threshold of superconductivity is calculated for arbitrary temperature, disorder strength, sample size and current and(or) magnetic field strength. Sample-size and magnetic field driven transition from normal metal phase to superconductivity has been studied. The superconductivity phase is not discussed., Comment: 12 pages, 13 figures, bugs fixed

The rigorous analysis of textbook result(Chiu and Quinn, 1974) gives unexpectedly the dramatic change of magnetoplasmon spectrum taking into account both the arbitrary dissipation and asymmetric off-plane structure of 2D system. For given wave vector the dissipation enhancement leads to decrease(increase) of magnetoplasmon frequency at low(high) magnetic field. At certain range of disorder the purely relaxational mode appears in magnetoplasmon spectrum. In strong magnetic fields the magnetoplasmon frequency falls to cyclotron resonance line even in presence of finite dissipation. The recent observation of 2D magnetoplasmon spectrum is consistent with our findings., Comment: 4+ pages, 3 figures

The melting condition for two-dimensional Wigner solid ( P.M. Platzman, H.Fukuyama, 1974) is shown to contain an error of a factor of $\pi$. The analysis of experimental data for apparent 2D metal-to-insulator transition shows that the Wigner solidification (B.Tanatar, D.M.Ceperley, 1989) has been never achieved. Within routine Fermi gas model both the metallic and insulating behavior of different 2D system for actual range of carrier densities and temperatures is explained., Comment: 4 pages, changes in fig.3

The applied voltage along a wire leads to a constant current density and, in turn, the azimuthal magnetic field. The absence of the radial current in a sample bulk requires nonzero radial(Hall) electric field to be present. We show that the longitudinal current itself is exactly that provided by the carriers drift in crossed azimuthal magnetic and Hall electric field. Nonzero carrier viscosity leads to nonuniform current flow dependent on the boundary condition at the inner wire wall. We find the general boundary condition accounting diamagnetic currents. At low temperatures the enhanced carrier viscosity leads to both the current and azimuthal magnetic field are pushed out the wire bulk towards the inner boundary. Simultaneously, the sample resistance strongly vanishes exhibiting a temperature driven threshold transition. Within low-current limit we calculate the threshold temperature for arbitrary carrier scattering and the sample size. For bulky sample and finite applied current our theory provides the universal phase transition diagram in terms of magnetic field vs temperature., Comment: 9 pages, 10 figures

The quantum capacitance of the monolayer graphene for arbitrary carrier density, magnetic field and temperature is found. The density dependence of the quantum capacitance is analyzed for magnetic field(temperature) is fixed(varied) and vice versa. The theory is compared with the experimental data., Comment: 5 pages, 6 figures, important changes to v2

Quantum Hall effect in 1,2-layer graphene is analyzed. The transverse and longitudinal resistivity are found to be universal functions of the filling factor and temperature. At fixed magnetic field mode the magneto-transport problem is resolved in the vicinity of the Dirac point., Comment: minor changes to v1, 10 pages, 11 nice figures

The dc voltage observed at low-temperatures in a 2D electron sample $without$ external excitation is accounted by the Schottky contact rectification of the noise generated in the measuring circuit. The rectified voltage is shown to depend on the asymmetry of the contact pair. The dependence of the rectified voltage on the noise amplitude first follows the trivial quadratic law, then exhibits a nearly linear behavior, and, finally, levels-off., Comment: 3.25 pages, 3 figures

The response of an ungated two-dimensional electron gas(2DEG) to an external electromagnetic excitation is analyzed. The possibility of creating a single-mode resonance detector operating in the terahertz frequency range is demonstrated., Comment: 5 pages 4 figures, minor v.1 changes

We analyze the current instability of the steady state with a direct current for an ungated two-dimensional(2D) electron layer for arbitrary current and the carrier scattering strength. We demonstrate the possibility of single-mode generator operating in terahertz frequency range., Comment: 3 pages, 2 figures

Taking into account both the scattering and the velocity saturation of carriers, we examine the "shallow-water" instability of the two-dimensional electron gas in a field effect transistor. It is shown that both the scattering (which is analogous to friction in a shallow-water channel) and the carrier velocity saturation lead to damping of the plasma wave instability. Threshold diagram of instability is calculated. The actual device parameters required for observation of plasma wave generation are compared with those reported in recent sub-terahertz emission experiments., Comment: 7 pages, 5 figures

The beating pattern of Shubnikov-de Haas oscillations in 2D electron system in the presence of a Rashba zero-field spin splitting is reproduced. It is shown, taking into account the Zeeman splitting, that the explicit formulae for the node position well describes the experimental data. The spin-orbit interaction strength obtained is found to be magnetic field independent in an agreement with the basic assumptions of the Rashba model., Comment: 4 pages, 2 figures

Recently, S.A.Mikhailov et al presented a theoretical study(cond-mat/0407364) concerning the electromagnetic response of a finite-width two-dimensional electron stripe. Surprisingly, in the above manuscript the magnetic field dependence of the magnetoplasmon spectrum(namely Fig.4) reproduces that reported for the first time in our paper(cond-mat/0405176, JETP Lett., 80, August 2004, in press). We believe that the above curious coincidence may result from the authors not to be informed enough., Comment: 1 page

Within dissipationless limit the magnetic field dependence of magnetoplasmon spectrum for unbounded 2DEG system found to intersect the cyclotron resonance line, and, then approaches the frequency given by light dispersion relation. Recent experiments done for macroscopic disc-shape 2DEG systems confirm theory expectations., Comment: 2 pages,2 figures

The beating pattern of Shubnikov-de Haas oscillations is reproduced in both the crossed and tilted magnetic field configuration and in presence of zero-field valley splitting in Si-MOSFET system. The consequences of IQHE in extremely dilute 2DEG are discussed., Comment: 4 pages, 4 figures

The complete set of Maxwell equations is represented by a single equation using Riemann-Silberstein complex vector of electromagnetic field. The consistent derivation of the Lorenz gauge condition is presented. We demonstrate that Fourier form of invariants ${\bf EB}$ and $E^{2}-B^{2}$ are proportional to dissipated power and equal to zero respectively., Comment: 3 pages,1 figure, CMD-EPS'20, S3Z203, Prague, July 19-23, (2004)

We demonstrate that N(S)-shape current-voltage characteristics proposed to explain zero-resistance state in Corbino(Hall bar) geometry 2DEG (cond-mat/0302063, cond-mat/0303530) cannot account essential features of radiation-induced magnetoresistance oscillations experiments., Comment: 1 page, 1 figure

We calculate the resistivity of 2D electron (hole) gas, taking into account the degeneracy and the thermal correction due to the combined Peltier and Seebeck effects. The resistivity is found to be universal function of temperature, expressed in units of $\frac{h}{e^{2}} (k_{F}l)^{-1}$. The giant parallel magnetiresistivity found to result from the spin and, if exists, valley splitting of the energy spectrum. Our analysis of compressibility and thermopower points to thermodynamic nature of metal-insulator transition in 2D systems., Comment: 5 pages, 4 figures, ICPS'26, D113, Edinburgh, UK

The resistivity components of 3D electron gas placed in quantizing magnetic field are calculated taking into account the correction caused by combined action of the Peltier and Seebeck thermoelectric effects. The longitudinal, transverse and the Hall magnetoresistivities exhibit familiar 1/H-period oscillations being universal functions of magnetic field and temperature., Comment: 3.14 pages, the only figure, Solid State Comm., 2014

We calculate the zero magnetic field resistivity, taking into account the degeneracy of the 2D electron (hole) gas and the thermal correction due to the combined Peltier and Seebeck effects. The resistivity is found to be universal function of temperature, expressed in units of $\frac{h}{e^{2}}% (k_{F}l)^{-1}$., Comment: 3 pages, 2 figures. submitted to PRL

The strongly nonlinear regime of Dyakonov-Shur instability is studied analytically and by computer simulations. The instability leads to high-amplitude stationary oscillations caused by shock wave formation in the FET channel. The numerically found shape and speed of the shock waves are well described in terms of the conventional hydrodynamics. The amplitude of stationary oscillations is determined., Comment: 5 pages, 4 figures, submitted to Phys.Rev.B

Based on a thermodynamic approach, we have calculated the resistivity of a 2D electron gas, assumed $dissipationless$ in a strong quantum limit. Standard measurements, with extra current leads, define the resistivity caused by a combination of Peltier and Seebeck effects. The current causes heating(cooling) at the first(second) sample contacts, due to the Peltier effect. The contact temperatures are different. The measured voltage is equal to the Peltier effect-induced thermoemf which is linear in current. As a result, the resistivity is non-zero as $I\to 0$. The resistivity is a universal function of magnetic field and temperature, expressed in fundamental units $h/e^{2}$. The universal features of magnetotransport data observed in experiment confirm our predictions., Comment: 11 pages, 3 figures, 1 table

We demonstrate that in strong quantum limit the thermoelectric Peltier effect could define the longitudinal resistivity of dissipationless two-dimensional electron(hole) gas. The current results in heating(cooling) at first(second) Hall bar sample contact due to Peltier effect. At small current the contacts temperatures are different, the temperature gradient is linear on current. The voltage swing downstream the current is proportional to Peltier effect induced thermopower. As a result, nonzero longitudinal resistivity is measured in experiment. The above effect could exist in 3D case., Comment: 5 pages, 3 figures, submitted to 5 pages, 3 figures, submitted to PRL

The standard ohmic measurements by means of two extra leads contain an additional thermal correction to resistance. The current results in heating(cooling) at first(second) sample contact due to Peltier effect. The contacts temperatures are different. The measured voltage is the sum of the ohmic voltage swing and Peltier effect induced thermopower which is linear on current. As a result, the thermal correction to resistance measured exists at $I\to 0$. The correction should be in comparison with ohmic resistance. Above some critical frequency dependent on thermal inertial effects the thermal correction disappears., Comment: 3 pages, 2 figures