35,693 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
Conductivity of suspended and non-suspended graphene at finite gate voltage
We compute the DC and the optical conductivity of graphene for finite values
of the chemical potential by taking into account the effect of disorder, due to
mid-gap states (unitary scatterers) and charged impurities, and the effect of
both optical and acoustic phonons. The disorder due to mid-gap states is
treated in the coherent potential approximation (CPA, a self-consistent
approach based on the Dyson equation), whereas that due to charged impurities
is also treated via the Dyson equation, with the self-energy computed using
second order perturbation theory. The effect of the phonons is also included
via the Dyson equation, with the self energy computed using first order
perturbation theory. The self-energy due to phonons is computed both using the
bare electronic Green's function and the full electronic Green's function,
although we show that the effect of disorder on the phonon-propagator is
negligible. Our results are in qualitative agreement with recent experiments.
Quantitative agreement could be obtained if one assumes water molelcules under
the graphene substrate. We also comment on the electron-hole asymmetry observed
in the DC conductivity of suspended graphene.Comment: 13 pages, 11 figure
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
Automatic learning of gait signatures for people identification
This work targets people identification in video based on the way they walk
(i.e. gait). While classical methods typically derive gait signatures from
sequences of binary silhouettes, in this work we explore the use of
convolutional neural networks (CNN) for learning high-level descriptors from
low-level motion features (i.e. optical flow components). We carry out a
thorough experimental evaluation of the proposed CNN architecture on the
challenging TUM-GAID dataset. The experimental results indicate that using
spatio-temporal cuboids of optical flow as input data for CNN allows to obtain
state-of-the-art results on the gait task with an image resolution eight times
lower than the previously reported results (i.e. 80x60 pixels).Comment: Proof of concept paper. Technical report on the use of ConvNets (CNN)
for gait recognition. Data and code:
http://www.uco.es/~in1majim/research/cnngaitof.htm
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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