940 research outputs found
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
Changes of metabolism in animals due to conditions of a purulent wound process while using photomineralisation as dressing tools
The aim of our research was to study the dynamics of the General biochemical parameters of blood of laboratory rats in accordance with the phases of the wound process using phytomineralsorbent
- …