234 research outputs found
Minimal conductivity of rippled graphene with topological disorder
We study the transport properties of a neutral graphene sheet with curved
regions induced or stabilized by topological defects. The proposed model gives
rise to Dirac fermions in a random magnetic field and in the random space
dependent Fermi velocity induced by the curvature. This last term leads to
singular long range correlated disorder with special characteristics. The Drude
minimal conductivity at zero energy is found to be inversely proportional to
the density of topological disorder, a signature of diffusive behavior.Comment: 12 pages, no figure
Topological insulating phases in mono and bilayer graphene
We analyze the influence of different quadratic interactions giving rise to
time reversal invariant topological insulating phases in mono and bilayer
graphene. We make use of the effective action formalism to determine the
dependence of the Chern Simons coefficient on the different interactions
Charge instabilities and topological phases in the extended Hubbard model on the honeycomb lattice with enlarged unit cell
We study spontaneous symmetry breaking in a system of spinless fermions in
the Honeycomb lattice paying special emphasis to the role of an enlarged unit
cell on time reversal symmetry broken phases. We use a tight binding model with
nearest neighbor hopping t and Hubbard interaction V1 and V2 and extract the
phase diagram as a function of electron density and interaction within a mean
field variational approach. The analysis completes the previous work done in
Phys. Rev. Lett. 107, 106402 (2011) where phases with non--trivial topological
properties were found with only a nearest neighbor interaction V1 in the
absence of charge decouplings. We see that the topological phases are
suppressed by the presence of metallic charge density fluctuations. The
addition of next to nearest neighbor interaction V2 restores the topological
non-trivial phases
Topological Fermi liquids from Coulomb interactions in the doped Honeycomb lattice
We get an anomalous Hall metallic state in the Honeycomb lattice with nearest
neighbors only arising as a spontaneously broken symmetry state from a local
nearest neighbor Coulomb interaction V . The key ingredient is to enlarge the
unit cell to host six atoms that permits Kekul\'e distortions and supports
self-consistent currents creating non trivial magnetic configurations with
total zero flux. We find within a variational mean field approach a metallic
phase with broken time reversal symmetry (T) very close in parameter space to a
Pomeranchuk instability. Within the T broken region the predominant
configuration is an anomalous Hall phase with non zero Hall conductivity, a
realization of a topological Fermi liquid. A T broken phase with zero Hall
conductivity is stable in a small region of the parameter space for lower
values of V
Charge inhomogeneities due to smooth ripples in graphene sheets
We study the effect of the curved ripples observed in the free standing
graphene samples on the electronic structure of the system. We model the
ripples as smooth curved bumps and compute the Green's function of the Dirac
fermions in the curved surface. Curved regions modify the Fermi velocity that
becomes a function of the point on the graphene surface and induce energy
dependent oscillations in the local density of states around the position of
the bump. The corrections are estimated to be of a few percent of the flat
density at the typical energies explored in local probes such as scanning
tunnel microscopy that should be able to observe the predicted correlation of
the morphology with the electronics. We discuss the connection of the present
work with the recent observation of charge anisotropy in graphene and propose
that it can be used as an experimental test of the curvature effects.Comment: 9 pages, 5 figures. v2: Abstract and discussion about experimental
consequences expande
Dirac fermions in a power-law-correlated random vector potential
We study localization properties of two-dimensional Dirac fermions subject to
a power-law-correlated random vector potential describing, e.g., the effect of
"ripples" in graphene. By using a variety of techniques (low-order perturbation
theory, self-consistent Born approximation, replicas, and supersymmetry) we
make a case for a possible complete localization of all the electronic states
and compute the density of states.Comment: Latex, 4+ page
Electronic properties of disclinated flexible membrane beyond the inextensional limit: Application to graphene
Gauge-theory approach to describe Dirac fermions on a disclinated flexible
membrane beyond the inextensional limit is formulated. The elastic membrane is
considered as an embedding of 2D surface into R^3. The disclination is
incorporated through an SO(2) gauge vortex located at the origin, which results
in a metric with a conical singularity. A smoothing of the conical singularity
is accounted for by replacing a disclinated rigid plane membrane with a
hyperboloid of near-zero curvature pierced at the tip by the SO(2) vortex. The
embedding parameters are chosen to match the solution to the von Karman
equations. A homogeneous part of that solution is shown to stabilize the
theory. The modification of the Landau states and density of electronic states
of the graphene membrane due to elasticity is discussed.Comment: 15 pages, Journal of Physics:Condensed Matter in pres
Revivals of quantum wave-packets in graphene
We investigate the propagation of wave-packets on graphene in a perpendicular
magnetic field and the appearance of collapses and revivals in the
time-evolution of an initially localised wave-packet. The wave-packet evolution
in graphene differs drastically from the one in an electron gas and shows a
rich revival structure similar to the dynamics of highly excited Rydberg
states.
We present a novel numerical wave-packet propagation scheme in order to solve
the effective single-particle Dirac-Hamiltonian of graphene and show how the
collapse and revival dynamics is affected by the presence of disorder. Our
effective numerical method is of general interest for the solution of the Dirac
equation in the presence of potentials and magnetic fields.Comment: 22 pages, 10 figures, 3 movies, to appear in New Journal of Physic
Continuous multi-criteria methods for crop and soil conservation planning on La Colacha (RĆo Cuarto, Province of Cordoba, Argentina)
Agro-areas of Arroyos Menores (La Colacha) west and south of Rand south of R?o Cuarto (Prov. of Cordoba, Argentina) basins are very fertile but have high soil loses. Extreme rain events, inundations and other severe erosions forming gullies demand urgently actions in this area to avoid soil degradation and erosion supporting good levels of agro production. The authors first improved hydrologic data on La Colacha, evaluated the systems of soil uses and actions that could be recommended considering the relevant aspects of the study area and applied decision support systems (DSS) with mathematic tools for planning of defences and uses of soils in these areas. These were conducted here using multi-criteria models, in multi-criteria decision making (MCDM); first of discrete MCDM to chose among global types of use of soils, and then of continuous MCDM to evaluate and optimize combined actions, including repartition of soil use and the necessary levels of works for soil conservation and for hydraulic management to conserve against erosion these basins. Relatively global solutions for La Colacha area have been defined and were optimised by Linear Programming in Goal Programming forms that are presented as Weighted or Lexicographic Goal Programming and as Compromise Programming. The decision methods used are described, indicating algorithms used, and examples for some representative scenarios on La Colacha area are given
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