Partial Kekule Ordering of Adatoms on Graphene

Electronic and transport properties of Graphene, a one-atom thick crystalline material, are sensitive to the presence of atoms adsorbed on its surface. An ensemble of randomly positioned adatoms, each serving as a scattering center, leads to the Bolzmann-Drude diffusion of charge determining the resistivity of the material. An important question, however, is whether the distribution of adatoms is always genuinely random. In this Article we demonstrate that a dilute adatoms on graphene may have a tendency towards a spatially correlated state with a hidden Kekule mosaic order. This effect emerges from the interaction between the adatoms mediated by the Friedel oscillations of the electron density in graphene. The onset of the ordered state, as the system is cooled below the critical temperature, is accompanied by the opening of a gap in the electronic spectrum of the material, dramatically changing its transport properties

Chiral tunneling and the Klein paradox in graphene

The so-called Klein paradox - unimpeded penetration of relativistic particles through high and wide potential barriers - is one of the most exotic and counterintuitive consequences of quantum electrodynamics (QED). The phenomenon is discussed in many contexts in particle, nuclear and astro- physics but direct tests of the Klein paradox using elementary particles have so far proved impossible. Here we show that the effect can be tested in a conceptually simple condensed-matter experiment by using electrostatic barriers in single- and bi-layer graphene. Due to the chiral nature of their quasiparticles, quantum tunneling in these materials becomes highly anisotropic, qualitatively different from the case of normal, nonrelativistic electrons. Massless Dirac fermions in graphene allow a close realization of Klein's gedanken experiment whereas massive chiral fermions in bilayer graphene offer an interesting complementary system that elucidates the basic physics involved.Comment: 15 pages, 4 figure

Tunneling conductance in strained graphene-based superconductor: Effect of asymmetric Weyl-Dirac fermions

Based on the BTK theory, we investigate the tunneling conductance in a uniaxially strained graphene-based normal metal (NG)/ barrier (I)/superconductor (SG) junctions. In the present model, we assume that depositing the conventional superconductor on the top of the uniaxially strained graphene, normal graphene may turn to superconducting graphene with the Cooper pairs formed by the asymmetric Weyl-Dirac electrons, the massless fermions with direction-dependent velocity. The highly asymmetrical velocity, vy/vx>>1, may be created by strain in the zigzag direction near the transition point between gapless and gapped graphene. In the case of the highly asymmetrical velocity, we find that the Andreev reflection strongly depends on the direction and the current perpendicular to the direction of strain can flow in the junction as if there was no barrier. Also, the current parallel to the direction of strain anomalously oscillates as a function of the gate voltage with very high frequency. Our predicted result is found as quite different from the feature of the quasiparticle tunneling in the unstrained graphene-based NG/I/SG conventional junction. This is because of the presence of the direction-dependent-velocity quasiparticles in the highly strained graphene system.Comment: 18 pages, 7 Figures; Eq.13 and 14 are correcte

The development of preparation and production management methods for excavation works in construction

© 2016, International Journal of Pharmacy and Technology. All rights reserved.Currently, there are several systems of building regulations. The types of applied manufacturing technologies increases at large volumes of construction works. Thus, the amount of applied equipment (machinery and mechanisms) also increases. When compressed terms of construction it is necessary to form an optimal structure of the building site, namely to determine the effective amount of engineers, machinery and workers. The main goal of this work is to develop the method of construction preparation and management using the example of excavation works. In order to create this work we used the method of empirical data collection, recorded on the construction sites directly and their further processing was performed (the assembling in complexes and the ranging by importance). The result of this work is the proposed method consisting of five algorithms. Algorithms select optimally a construction group among the construction machines and mechanisms owned by a company. An engineering staff and workers are attributed to them. The algorithm works according to the principle of minimal downtime and maximum productivity. The effect is provided by the bringing in of idle machines and mechanisms for supporting works. These algorithms can be used both by large and small construction companies

Nonmagnetic-Defect-Induced Magnetism in Graphene

It is shown that a strong impurity potential induces short-range antiferromagnetic (ferrimagnetic) order around itself in a Hubbard model on a half-filled honeycomb lattice. This implies that short-range magnetic order is induced in monolayer graphene by a nonmagnetic defect such as a vacancy with full hydrogen termination or a chemisorption defect.Comment: 5 pages, 8 figure

Development of the company due to forming of innovative structure

© Medwell Journals, 2017. The study reveals the essence of the region's innovation infrastructure as a factor in increasing the efficiency of industrial enterprises. The relevance of the topic is due to the fact that the path of innovative development of industrial enterprises in the Russian Federation based on knowledge, on the change in the economic structure in favor of high-tech industries to increase human capital becomes the only possible way of development in the modern economics. Today, innovation is a component of the business process for companies that are focused on the preservation and strengthening of its position in the markets, especially in the long term. Moreover, innovation is based not only on inventions but on the efficient utilization of resources resulting from scientific and technological progress. The study concludes that the functioning of a modern tool of management in the conditions of growing changes in the external environment acts as a methodology of infrastructural development. The choice of directions and defining the scope of infrastructure development that takes place within the association of industrial enterprises are of the particular importance. The need for innovation in the field of infrastructure solutions plan arises when independent activities related to innovation activities can not achieve their goals. The winner is the company that is able to determine the time, place and subjects of association. Therefore, an adequate regulation of the relationship of enterprises engaged in innovation is the key of success in providing innovative economy. This focus of the new economic thinking requires a fundamental revision of the methodological approach used and the applied methodological tools. The problem of the Russian economy transition on an innovative path of development has been very relevant in the pre-crisis period and remains the same nowadays. It is impossible to overcome the country's dependence on conditions in the world without handling this problem, especially in the oil market. Active policy of innovative development of the economy must not take second place to fight the crisis. Only innovative renewal of fixed capital and the introduction of new technologies in the production of goods are able to provide a valid output of the economy from the stage of the crisis on the upward trajectory of its functioning and development

Electronic correlations in promising room-temperature superconductor Pb9_9Cu(PO4_4)6_6O: a DFT+DMFT study

We present results of the first investigations on the correlated nature of electronic states that cross the Fermi level in Pb$_9$Cu(PO$_4$)$_6$O aka LK-99 obtained within the DFT + DMFT approach. Coulomb correlations between Cu-$d$ electrons led to the opening of the band gap between the extra-O $p$ and Cu $d_{xz}/d_{yz}$ states. We state that oxygen $p$ states play a significant role in the electronic properties of LK-99. We also assume that doping with electrons is necessary to turn the stoichiometric Pb$_9$Cu(PO$_4$)$_6$O into conducting state

The quantum Hall effect in graphene - a theoretical perspective

This short theoretical review deals with some essential ingredients for the understanding of the quantum Hall effect in graphene in comparison with the effect in conventional two-dimensional electron systems with a parabolic band dispersion. The main difference between the two systems stems from the "ultra-relativistic" character of the low-energy carriers in graphene, which are described in terms of a Dirac equation, as compared to the non-relativistic Schr\"odinger equation used for electrons with a parabolic band dispersion. In spite of this fundamental difference, the Hall resistance quantisation is universal in the sense that it is given in terms of the universal constant h/e^2 and an integer number, regardless of whether the charge carriers are characterised by Galilean or Lorentz invariance, for non-relativistic or relativistic carriers, respectively.Comment: 9 pages, 4 figures; brief review article for Comptes Rendus de l'Academie des Sciences; references added with respect to previous versio

Edge states of graphene bilayer strip

The electronic structure of the zig-zag bilayer strip is analyzed. The electronic spectra of the bilayer strip is computed. The dependence of the edge state band flatness on the bilayer width is found. The density of states at the Fermi level is analytically computed. It is shown that it has the singularity which depends on the width of the bilayer strip. There is also asymmetry in the density of states below and above the Fermi energy.Comment: 9 page