31,373 research outputs found
Algebraic solution of a graphene layer in a transverse electric and perpendicular magnetic fields
We present an exact algebraic solution of a single graphene plane in
transverse electric and perpendicular magnetic fields. The method presented
gives both the eigen-values and the eigen-functions of the graphene plane. It
is shown that the eigen-states of the problem can be casted in terms of
coherent states, which appears in a natural way from the formalism.Comment: 11 pages, 5 figures, accepted for publication in Journal of Physics
Condensed Matte
Bilayer graphene: gap tunability and edge properties
Bilayer graphene -- two coupled single graphene layers stacked as in graphite
-- provides the only known semiconductor with a gap that can be tuned
externally through electric field effect. Here we use a tight binding approach
to study how the gap changes with the applied electric field. Within a parallel
plate capacitor model and taking into account screening of the external field,
we describe real back gated and/or chemically doped bilayer devices. We show
that a gap between zero and midinfrared energies can be induced and externally
tuned in these devices, making bilayer graphene very appealing from the point
of view of applications. However, applications to nanotechnology require
careful treatment of the effect of sample boundaries. This being particularly
true in graphene, where the presence of edge states at zero energy -- the Fermi
level of the undoped system -- has been extensively reported. Here we show that
also bilayer graphene supports surface states localized at zigzag edges. The
presence of two layers, however, allows for a new type of edge state which
shows an enhanced penetration into the bulk and gives rise to band crossing
phenomenon inside the gap of the biased bilayer system.Comment: 8 pages, 3 fugures, Proceedings of the International Conference on
Theoretical Physics: Dubna-Nano200
Inducing energy gaps in graphene monolayer and bilayer
In this paper we propose a mechanism for the induction of energy gaps in the
spectrum of graphene and its bilayer, when both these materials are covered
with water and ammonia molecules. The energy gaps obtained are within the range
20-30 meV, values compatible to those found in experimental studies of graphene
bilayer. We further show that the binding energies are large enough for the
adsorption of the molecules to be maintained even at room temperature
Modeling non-thermal emission from stellar bow shocks
Runaway O- and early B-type stars passing throughout the interstellar medium
at supersonic velocities and characterized by strong stellar winds may produce
bow shocks that can serve as particle acceleration sites. Previous theoretical
models predict the production of high energy photons by non-thermal radiative
processes, but their efficiency is still debated. We aim to test and explain
the possibility of emission from the bow shocks formed by runaway stars
traveling through the interstellar medium by using previous theoretical models.
We apply our model to AE Aurigae, the first reported star with an X-ray
detected bow shock, to BD+43 3654, in which the observations failed in
detecting high energy emission, and to the transition phase of a supergiant
star in the late stages of its life.From our analysis, we confirm that the
X-ray emission from the bow shock produced by AE Aurigae can be explained by
inverse Compton processes involving the infrared photons of the heated dust. We
also predict low high energy flux emission from the bow shock produced by BD+43
3654, and the possibility of high energy emission from the bow shock formed by
a supergiant star during the transition phase from blue to red supergiant.Bow
shock formed by different type of runaway stars are revealed as a new possible
source of high energy photons in our neighbourhood
Variable exponent Sobolev spaces associated with Jacobi expansions
In this paper we define variable exponent Sobolev spaces associated with
Jacobi expansions. We prove that our generalized Sobolev spaces can be
characterized as variable exponent potential spaces and as variable exponent
Triebel-Lizorkin type spaces.Comment: 30 pages, small typos corrected in the introductio
Localized states at zigzag edges of bilayer graphene
We report the existence of zero energy surface states localized at zigzag
edges of bilayer graphene. Working within the tight-binding approximation we
derive the analytic solution for the wavefunctions of these peculiar surface
states. It is shown that zero energy edge states in bilayer graphene can be
divided into two families: (i) states living only on a single plane, equivalent
to surface states in monolayer graphene; (ii) states with finite amplitude over
the two layers, with an enhanced penetration into the bulk. The bulk and
surface (edge) electronic structure of bilayer graphene nanoribbons is also
studied, both in the absence and in the presence of a bias voltage between
planes.Comment: 4 pages, 5 figure
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