38,305 research outputs found
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
The role of pressure on the magnetism of bilayer graphene
We study the effect of pressure on the localized magnetic moments induced by
vacancies in bilayer graphene in the presence of topological defects breaking
the bipartite nature of the lattice. By using a mean-field Hubbard model we
address the two inequivalent types of vacancies that appear in the Bernal
stacking bilayer graphene. We find that by applying pressure in the direction
perpendicular to the layers the critical value of the Hubbard interaction
needed to polarize the system decreases. The effect is particularly enhanced
for one type of vacancies, and admits straightforward generalization to
multilayer graphene in Bernal stacking and graphite. The present results
clearly demonstrate that the magnetic behavior of multilayer graphene can be
affected by mechanical transverse deformation
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
Beyond the soft photon approximation in radiative production and decay of charged vector mesons
We study the effects of model-dependent contributions and the electric
quadrupole moment of vector mesons in the decays and
. Their interference with the amplitude originating
from the radiation due to electric charges vanishes for photons emitted
collinearly to the charged particle in the final state. This brings further
support to our claim in previous works, that measurements of the photon energy
spectrum for nearly collinear photons in those decays are suitable for a first
measurement of the magnetic dipole moment of charged vector mesons.Comment: 13 pages, 2 eps figures, Latex. Accepted for publication in Journal
of Physics G: Nuclear and Particle Physics(2001
Structure-dependent radiative corrections to phi -> K^+K^-/K_LK_S decays
Current predictions for the ratio of phi -> K^+K^-/K_LK_S decay rates exceed
the corresponding experimental value in about five standard deviations. By far,
the dominant sources of isospin breaking to this ratio are the phase-space
(52%) and the electromagnetic radiative (4.3%, computed within scalar QED)
corrections. Here we estimate the effects of the electromagnetic structure of
kaons and other model-dependent contributions into the radiative corrections.Comment: 8 pages, Latex, 2 .eps figure
Quantum quench dynamics and population inversion in bilayer graphene
The gap in bilayer graphene (BLG) can directly be controlled by a
perpendicular electric field. By tuning the field through zero at a finite rate
in neutral BLG, excited states are produced. Due to screening, the resulting
dynamics is determined by coupled non-linear Landau-Zener models. The generated
defect density agrees with Kibble-Zurek theory in the presence of subleading
logarithmic corrections. After the quench, population inversion occurs for
wavevectors close to the Dirac point. This could, at least in principle provide
a coherent source of infra-red radiation with tunable spectral properties
(frequency and broadening). Cold atoms with quadratic band crossing exhibit the
same dynamics.Comment: 6 pages, 2 figures, 1 tabl
- …