Conductivity of epitaxial and CVD graphene with correlated line defects

Transport properties of single-layer graphene with correlated one-dimensional defects are studied using the time-dependent real-space Kubo-Greenwood formalism. Such defects are present in epitaxial graphene, comprising atomic terraces and steps due to the substrate morphology, and in polycrystalline chemically-vapor-deposited (CVD) graphene due to the grain boundaries, composed of a periodic array of dislocations, or quasi-periodic nanoripples originated from the metal substrate. The extended line defects are described by the long-range Lorentzian-type scattering potential. The dc conductivity is calculated numerically for different cases of distribution of line defects. This includes a random (uncorrelated) and a correlated distribution with a prevailing direction in the orientation of lines. The anisotropy of the conductivity along and across the line defects is revealed, which agrees with experimental measurements for epitaxial graphene grown on SiC. We performed a detailed study of the conductivity for different defect correlations, introducing the correlation angle alpha_max (i.e. the maximum possible angle between any two lines). We find that for a given electron density, the relative enhancement of the conductivity for the case of fully correlated line defects in comparison to the case of uncorrelated ones is larger for a higher defect density. Finally, we study the conductivity of realistic samples where both extended line defects as well as point-like scatterers such as adatoms and charged impurities are presented.Comment: 8 pages, 7 figure

Influence of correlated impurities on conductivity of graphene sheets: Time-dependent real-space Kubo approach

Exact numerical calculations of the conductivity of graphene sheets with random and correlated distributions of disorders have been performed using the time-dependent real-space Kubo formalism. The disorder was modeled by the long-range Gaussian potential describing screened charged impurities and by the short-range potential describing neutral adatoms both in the weak and strong scattering regime. Our central result is that correlation in the spatial distribution for the strong short-range scatterers and for the long-range Gaussian potential do not lead to any enhancement of the conductivity in comparison to the uncorrelated case. Our results strongly indicate that the temperature enhancement of the conductivity reported in the recent study (Yan and Fuhrer, Phys. Rev. Lett. 107, 206601 (2011)) and attributed to the effect of dopant correlations was most likely caused by other factors not related to the correlations in the scattering potential.Comment: 14 pages, 10 figure

BRST structure of non-linear superalgebras

In this paper we analyse the structure of the BRST charge of nonlinear superalgebras. We consider quadratic non-linear superalgebras where a commutator (in terms of (super) Poisson brackets) of the generators is a quadratic polynomial of the generators. We find the explicit form of the BRST charge up to cubic order in Faddeev-Popov ghost fields for arbitrary quadratic nonlinear superalgebras. We point out the existence of constraints on structure constants of the superalgebra when the nilpotent BRST charge is quadratic in Faddeev-Popov ghost fields. The general results are illustrated by simple examples of superalgebras.Comment: 15 pages, Latex, references added, misprints corrected, comments adde

Radio Broadcasting Experience and Development Prospects (European Scientific Dialogue)

The paper presents an analysis of various opinions concerning radio-industry development issues, given new IT processes implemented in mass media. The authors study the technological evolution of radio broadcasting in terms of analyzing its main development stages. They provide an assessment of listeners’ high confidence in radio broadcasts as compared to other mass media sources. Focus is placed on promoting sonic brands in the sphere of media-communication. The researchers also pay special attention to podcasting as a new way to listen to audio-content. The advantages and possible consequences of podcasting influence on radio-industry are assessed. The research is based on the expert discussion on radio broadcasting issues which took place at “Radiodays Europe 2019”