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We investigate the effect of surface reconstruction and strain on diffusion of adsorbed Ge atoms on Ge$(111)\textrm{-}5\times5$ and Ge$(111)\textrm{-}7\times7$ surfaces by means of first principles calculations. Stable adsorption sites, their energies, diffusion paths, and corresponding activation barriers are reported. We demonstrate that the decisive migration path is located near the corner holes of surface structures, and they are associated with formation of weak bonds between the adsorbed Ge atom and surface dimers (within the $5\times5$ or $7\times7$ structures). The results show that Ge diffusion rates on $5\times5$ and $7\times7$ reconstructed Ge$(111)$ surfaces should be similar. Conversely, the diffusion barrier on a compressively strained Ge$(111)$ surface is considerably higher than that on a strain-free surface, thus explaining previous experimental results. Comparable diffusion rates on $5\times5$ and $7\times7$ reconstructed surfaces are explained by the identical local atomic arrangements of these structures. The increase of the migration barrier on a strained surface is explained by dimer bond strengthening upon surface compression, along with a weakening of bonds between the adsorbed Ge and dimer atoms.

The atomic structure of well-ordered single steps on the Si(111)-\sqrt{3}\times\sqrt{3}-Sn surface and the dynamics of Sn adatoms in the vicinity of these steps was studied. The work was performed using low-temperature scanning tunneling microscopy (STM) and ab initio calculations based on the density-functional theory. The STM tip was used to record the tunneling current versus time on top of oscillating adatoms, keeping the feedback loop turned off. The dynamics of adatoms, detected as the telegraph noise present in the tunneling current, was registered near the steps at 80 K. The atomic structure model of the single steps consisting of Sn atomic chains along the steps was developed. This structure leads to the formation of potential double wells near the steps acting as traps for Sn atoms and explains the fluctuating current recorded in these areas., Comment: 9 pages, 8 figures

We report on the observation of the giant photoconductance of a quantum point contact (QPC) in tunneling regime excited by terahertz radiation. Studied QPCs are formed in a GaAs/AlGaAs heterostructure with a high-electron-mobility two-dimensional electron gas. We demonstrate that irradiation of strongly negatively biased QPCs by laser radiation with frequency f = 0.69 THz and intensity 50 mW/cm^2 results in two orders of magnitude enhancement of the QPC conductance. The effect has a superlinear intensity dependence and increases with the dark conductivity decrease. It is also characterized by strong polarization and frequency dependencies. We demonstrate that all experimental findings can be well explained by the photon-mediated tunneling through the QPC. Corresponding calculations are in a good agreement with the experiment., Comment: 8 pages, 8 figures

The boundary problem about behavior (oscillations) of the electronic plasmas with arbitrary degree of degeneration of electronic gas in half-space with specular boundary conditions is analytically solved. The kinetic equation of Vlasov--Boltzmann with integral of collisions of type BGK (Bhatnagar, Gross, Krook) and Maxwell equation for electric field are applied. Distribution function for electrons and electric field in plasma in the form of expansion under eigen solutions of the initial system of equations are received. Coefficients of these expansions are found by means of the boundary conditions., Comment: 16 pages, 4 figures

We have studied the magnetoresistance of the quantum point contact fabricated on the high mobility two-dimensional electron gas (2DEG) exposed to microwave irradiation. The resistance reveals giant $B$-periodic oscillations with the relative amplitude $\Delta R/R$ of up to $700$\% resulting from the propagation and interference of the edge magnetoplasmons (EMPs) in the sample. This giant photoconductance is attributed to the considerably large local electron density modulation in the vicinity of the point contact. We have also analyzed the oscillation periods $\Delta B$ of the resistance oscillations and, comparing the data with the EMP theory, extracted the EMP interference length $L$. We have found that the length $L$ substantially exceeds the distance between the contact leads but rather corresponds to the distance between metallic contact pads measured along the edge of the 2DEG. This resolves existing controversy in the literature and should help to properly design highly sensitive microwave and terahertz spectrometers based on the discussed effect., Comment: 5 pages, 5 figures

Classical plasma with arbitrary degree of degeneration of electronic gas is considered. In plasma N (N>2) collinear electromagnatic waves are propagated. It is required to find the response of plasma to these waves. Distribution function in square-law approximation on quantities of two small parameters from Vlasov equation is received. The formula for electric current calculation is deduced. It is demonstrated that the nonlinearity account leads to occurrence of the longitudinal electric current directed along a wave vector. This longitudinal current is orthogonal to the known transversal current received at the linear analysis. The case of small values of wave number is considered., Comment: 15 pages, 0 figures. arXiv admin note: substantial text overlap with arXiv:1612.06087

The boundary problem about behaviour (oscillations) of the electronic plasmas with arbitrary degree of degeneration of electronic gas in half-space with diffusion boundary conditions is analytically solved. The kinetic equation of Vlasov - Boltzmann with integral of collisions of type BGK (Bhatnagar, Gross, Krook) and Maxwell equation for electric field are applied. Distribution function for electrons and electric field in plasma in the form of expansion under eigen solutions of the initial system of equations are received. Coefficients of these expansions are found by means of the boundary conditions., Comment: in Russian; 37 pages, 5 figures

Quantum plasma with arbitrary degree of degeneration of electronic gas is considered. In plasma N (N>2) external electromagnetic waves are propagated. It is required to find the response of plasma to these waves. From kinetic Wigner equation for quantum collisionless plasmas distribution function in square-law approach on quantities of vector potentials of N electric fields is received. The formula for electric current calculation is deduced at arbitrary temperature, i.e. at arbitrary degree of degeneration of electronic gas. It is shown, that the nonlinearity account leads to occurrence of the longitudinal electric current directed along a wave vector. This longitudinal current is orthogonal to the known transversal current received at the linear analysis. The case of small values of wave number is considered. It is shown, that in case of small values of wave numbers the longitudinal current in quantum plasma coincides with a longitudinal current in classical plasma., Comment: 28 pages, 0 figures

The analytical solution of the boundary problem on behaviour (oscillations) of the electronic plasmas with arbitrary degree of degeneration of electronic gas in a slab of the conducting medium is received. The kinetic Vlasov---Boltzmann equation with integral of collisions type BGK (Bhatnagar, Gross and Krook) and Maxwell equation for electric field are applied. Mirror (reflections) boundary conditions are used., Comment: 22 pages, in Russian, 3 figures

One of classical boundary problems of the kinetic theory (a problem about thermal sliding) of the rarefied gas along a flat firm surface is considered. Kinetic Boltzmann equation with model integral of collisions BGK (Bhatnagar, Gross, Krook) is used. As boundary conditions the boundary Maxwell conditions (mirror-diffuse) are used. The generalized method of a source is applied to the problem decision. Comparison with earlier received results is spent., Comment: 15 pages, 0 figures, Article will be published in "Bulletin of the Moscow State Regional University. Series Physics and Mathematics", No. 1, 2016

In the present work the second Stokes problem about behaviour of the rarefied gas filling half-space is formulated. A plane limiting half-space makes harmonious fluctuations with variable amplitude in the plane. The amplitude changes on the exponential law. The kinetic equation with model integral of collisions in the form $\tau$-model is used. The case of diffusion reflexions of gas molecules from a wall is considered. Eigen solutions (continuous modes) of the initial kinetic equation corresponding to the continuous spectrum are searched. Properties of dispersion function are studied. It is investigated the discrete spectrum of the problem consisting of zero of the dispersion functions in the complex plane. It is shown, that number of zero of dispersion function to equally doubled index of problem coefficient. The problem coefficient is understood as the relation of boundary values of dispersion function from above and from below on the real axis. Further are eigen solutions (discrete modes) of the initial kinetic equation corresponding to the discrete spectrum are searched. In the end of work the general solution of the kinetic equation in the form expansion under eigen solutions with unknown coefficients corresponding to discrete and continuous spectra is constructed., Comment: 32 pages, in Russian, 8 figures

Earlier electron influence on sound absorption in metal on basis of the assumption of deformation of Fermi-surfaces under the influence of a sound wave was considered. In the present work other approach to this problem will be considered. Our approach based on the account of dynamic (kinetic) interaction of electronic gas with lattice fluctuations. The analysis of influence of electric field on process of attenuation of sound fluctuations is carried out. It is shown that in the long-wave limit this influence is essential., Comment: 34 pages, 11 figures

The second Stokes problem about behavior of the viscous fluid (matter) filling half-space is considered. A flat surface limiting half-space makes harmonious oscillations in the eigen plane. The equations of mechanics of the continuous environment are used. It is shown, that in considered process there is the temperature difference between temperature of a surface and temperature environments far from a surface. Usually similar difference is called as temperature jump. The method of small parameter is applied. Temperature jump in the second approach is found out., Comment: 8 pages, 0 figures

Quantum plasma with arbitrary degree degeneration of electronic gas is considered. Plasma is in two external electromagnetic fields. It is required to find the plasma response on this fields. From Wigner kinetic equation for the quantum collisionless plasmas distribution function in square-law approach on sizes of vector potentials of two electric fields is received. The formula for calculation electric current at any temperature (any degree of degeneration of electronic gas) is deduced. This formula contains an one-dimensional quadrature. It is shown, that the nonlinearity account leads to occurrence the longitudinal electric current directed along a wave vectors. This longitudinal current is orthogonal to a known transversal current, received at the linear analysis. The case of small values of wave numbers is considered. It is shown, that in case of small values of wave numbers a longitudinal current in quantum plasma coincides with a longitudinal current in classical plasma., Comment: 26 pages, in Russian. 0 figures

From kinetic Vlasov equation for collisional plasmas distribution function in square-law approximation on sizes of intensivities of electric fields is received. The known integral of collisions of relaxation type, so-called BGK (Bhatnagar, Gross, Krook) integral of collisions is considered. The formula for calculation electric current at any temperature (any degree of degeneration of electronic gas) is deduced. This formula contains an one-dimensional quadrature. It is shown, that the nonlinearity account leads to occurrence the longitudinal electric current directed along a wave vector. This longitudinal current is orthogonal to a known transversal classical current, received at the linear analysis. When frequency of collisions tends to the zero, all received results for collisional plasmas pass in corresponding formulas for collisionless plasmas. The case of small values of wave number is considered. It is shown, that the received quantity of longitudinal current at aspiration of frequency of collisions to zero also passes in corresponding expression of current for collisionless plasmas. Graphic comparison of dimensionless quantity of current depending on wave number, frequency of oscillations of electromagnetic field and frequencies of electron collisions with plasma particles is carry out., Comment: 33 pages, in Russian, 8 figures. arXiv admin note: substantial text overlap with arXiv:1505.06796

Classical plasma with any degree degeneration of electronic gas is considered. In plasma two external electromagnetic field are propagation. It is required to find the plasma response on these fields. From kinetic Vlasov equation for collisionless plasmas distribution function in square-law approximation on sizes of intensivities of two electric fields is received. The formula for calculation electric current at any temperature (any degree of degeneration electronic gas) is deduced. This formula contains an one-dimensional quadrature. It is shown, that the nonlinearity account leads to occurrence the longitudinal electric current directed along a wave vector. This longitudinal current is perpendicular to known tranversal classical current, received at the linear analysis. The case of small values of wave number is considered. Graphic comparison of dimensionless size of the current depending on wave number and frequency of oscillation of the electromagnetic fields is carry out., Comment: 22 pages, in Russian, 8 figures

Kinetic Vlasov equation for collisional Maxwellian plasmas is used. Collision integral of BGK (Bhatnagar, Gross and Krook) type is applied. From Vlasov equation we find distribution function of electrons in square-law approximation on size of transversal electric field. The formula for electric current calculation is deduced. This formula contains an one-dimensional quadrature. It is shown, that nonlinearity leads to revealing of the longitudinal electric current directed along a wave vector. This longitudinal current is perpendicular to known so-called transversal classical current. The classical current turns out at the linear analysis. The longitudinal current in case of small values of wave numbers is calculated. When frequency of collisions tends to zero, all received formulas for collisional plasmas pass in the known corresponding results for collisionless plasmas. Graphic research of dimensionless density of a current is carried out., Comment: 20 pages, 6 figures

Kinetic Vlasov-Boltzmann equation for degenerate collisional plasmas with integral of collisions of relaxation type BGK (Bhatnagar, Gross and Krook) is used. Square-law expansion on size of intensity of electric field for kinetic equation, Lorentz's force and integral of collisions is considered. It is shown, that nonlinearity leads to generation of the longitudinal electric current directed along a wave vector. Longitudinal current is perpendicular to the known transversal classical current received at the linear analysis. The case of small values of wave number is considered. When frequency of collisions tends to the zero, all received results for collisional pass plasmas in corresponding results for collisionless plasmas. Graphic research of the real and imaginary part current density is carried out., Comment: 21 pages, in Russian. 6 figures

Kinetic Vlasov equation for collisional plasmas with BGK (Bhatnagar-Gross-Krook) collision integral is used. The case of arbitrary temperature (i.e. arbitrary degree of degeneration of electronic gas) is considered. From kinetic Vlasov equation the distribution function in square-law approximation on size of transversal electromagnetic field is received. The formula for calculation electric current is deduced. This formula contains one-dimension quadrature. It is shown, that the nonlinearity account leads to occurrence the longitudinal electric current directed along the wave vector. This longitudinal current is perpendicular to the known transversal classical current, received at the linear analysis. When frequency of collisions tends to zero, all received results for collisional plasma pass in known corresponding formulas for collisionless plasma. The case of small values of wave number is considered. It is shown, that the received quantity of longitudinal current at tendency of frequency of collisions to zero also passes in known corresponding expression of current for collisionless plasmas. Graphic research of dimensionless density of the current depending on wave number, frequency of oscillations of electromagnetic field and frequency of electron collisions with plasma particles is carried out., Comment: 22 pages, 6 figures

The analysis of nonlinear interaction of transversal electromagnetic field with degenerate collisionless classical and quantum plasmas is carried out. Formulas for calculation electric current in degenerate collisionless classical and quantum plasmas are deduced. It has appeared, that the nonlinearity account leads to occurrence of longitudinal electric current directed along a wave vector. This second current is orthogonal to the known transversal current, received at the classical linear analysis. Graphic comparison of density of electric current for classical degenerate Fermi plasmas and Fermi-Dirac plasmas (plasmas with any degree of degeneration of electronic gas) is carried out. Graphic comparison of density of electric current for classical and quantum degenerate plasmas is carried out. Also comparison of dependence of density of electric current of quantum degenerate plasmas from dimensionless wave number at various values of dimensionless frequency of oscillations of electromagnetic field is carried out., Comment: 26 pages, 9 figures

The analysis of nonlinear interaction of transversal electromagnetic field with Maxwellian collisionless classical and quntum plasmas is carried out. Formulas for calculation electric current in Maxwellian collisionless classical and quntum plasmas are deduced. It has appeared, that the nonlinearity account leads to occurrence of the longitudinal electric current directed along a wave vector. This second current is orthogonal to the known transversal current, received at the classical linear analysis. Graphic comparison of density of electric current for classical Maxwellian plasmas and Fermi---Dirac plasmas (plasmas with any degree of degeneration of electronic gas) is carried out. Graphic comparison of density of electric current for classical and quantum Maxwellian plasmas is carried out. Also comparison of dependence of density of electric current of quantum Maxwellian plasmas from dimensionless wave number at various values of dimensionless frequency of oscillations of electromagnetic field is carried out., Comment: 18 pages, 6 figures. arXiv admin note: substantial text overlap with arXiv:1502.04581

From Vlasov kinetic equation for collisionless plasmas distribution function in square-law approximation on size of electromagnetic field is received. Formulas for calculation electric current at any temperature (any degree of degeneration of electronic gas) are deduced. The case of small values of the wave numbers is considered. It is shown, that the nonlinearity account leads to occurrence the longitudinal electric current directed along a wave vector. This longitudinal current orthogonal to known transversal classical current, received at the linear analysis. From the kinetic equation with Wigner integral for collisionless quantum plasma distribution function is received in square-law on vector potential approximation. Formulas for calculation electric current at any temperature are deduced. The case of small values of wave number is considered. It is shown, that size of a longitudinal current at small values of wave number and for classical plasma and for quantum plasma coincide. Graphic comparison of dimensionless size of a current quantum and classical plasma is made., Comment: 27 pages, 10 figures