24,281 research outputs found
Charge confinement and Klein tunneling from doping graphene
In the present work, we investigate how structural defects in graphene can
change its transport properties. In particular, we show that breaking of the
sublattice symmetry in a graphene monolayer overcomes the Klein effect, leading
to confined states of massless Dirac fermions. Experimentally, this corresponds
to chemical bonding of foreign atoms to carbon atoms, which attach themselves
to preferential positions on one of the two sublattices. In addition, we
consider the scattering off a tensor barrier, which describes the rotation of
the honeycomb cells of a given region around an axis perpendicular to the
graphene layer. We demonstrate that in this case the intervalley mixing between
the Dirac points emerges, and that Klein tunneling occurs.Comment: 11 pages, 5 figure
Broad Histogram Monte Carlo
We propose a new Monte Carlo technique in which the degeneracy of energy
states is obtained with a Markovian process analogous to that of Metropolis
used currently in canonical simulations. The obtained histograms are much
broader than those of the canonical histogram technique studied by Ferrenberg
and Swendsen. Thus we can reliably reconstruct thermodynamic functions over a
much larger temperature scale also away from the critical point. We show for
the two-dimensional Ising model how our new method reproduces exact results
more accurately and using less computer time than the conventional histogram
method. We also show data in three dimensions for the Ising ferromagnet and the
Edwards Anderson spin glass.Comment: 6 pages of a TeX file with 4 PS figures. Related papers at
http://www.if.uff.br/~tjp
Simulation for competition of languages with an ageing sexual population
Recently, individual-based models originally used for biological purposes
revealed interesting insights into processes of the competition of languages.
Within this new field of population dynamics a model considering sexual
populations with ageing is presented. The agents are situated on a lattice and
each one speaks one of two languages or both. The stability and quantitative
structure of an interface between two regions, initially speaking different
languages, is studied. We find that individuals speaking both languages do not
prefer any of these regions and have a different age structure than individuals
speaking only one language.Comment: submitted to International Journal of Modern Physics
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