16,311 research outputs found
Gaped graphene bilayer: disorder and magnetic field effects
Double layer graphene is a gapless semiconductor which develops a finite gap
when the layers are placed at different electrostatic potentials. We study,
within the tight-biding approximation, the electronic properties of the gaped
graphene bilayer in the presence of disorder, perpendicular magnetic field, and
transverse electric field. We show that the gap is rather stable in the
presence of diagonal disorder. We compute the cyclotron effective mass in the
semi-classical approximation, valid at low magnetic fields. Landau level
formation is clearly seen in zigzag and armchair ribbons of the gaped bilayer
at intermediate magnetic fields.Comment: 5 pages, 4 figure
Quantum Hall activation gaps in bilayer graphene
We have measured the quantum Hall activation gaps in bilayer graphene at
filling factors and in high magnetic fields up to 30 T.
We find that energy levels can be described by a 4-band relativistic hyperbolic
dispersion. The Landau level width is found to contain a field independent
background due to an intrinsic level broadening and a component which increases
linearly with magnetic field.Comment: 4 pages, accepted version (just removed a few typos), will appear as
Fast Track Communication in Solid State Commu
Supersymmetry and Correlated Electrons in Graphene Quantum Hall Effect
We present a supersymmetric description of the quantum Hall effect (QHE) in
graphene. The noninteracting system is supersymmetric separately at the
so-called K and K' points of the Brillouin zone corners. Its essential
consequence is that the energy levels and the Landau levels are different
objects in graphene QHE. Each energy level has a four-fold degeneracy within
the noninteracting theory. With the Coulomb interaction included, an excitonic
gap opens in the zero-energy state, while each nonzero energy level splits into
two levels since up-spin and down-spin electrons come from different Landau
levels. We argue the emergence of the plateaux at for small
magnetic field and at , , for large with
natural numbers.Comment: 5 pages, 2 figure
Zitterbewegung, chirality, and minimal conductivity in graphene
It has been recently demonstrated experimentally that graphene, or
single-layer carbon, is a gapless semiconductor with massless Dirac energy
spectrum. A finite conductivity per channel of order of in the limit
of zero temperature and zero charge carrier density is one of the striking
features of this system. Here we analyze this peculiarity based on the Kubo and
Landauer formulas. The appearance of a finite conductivity without scattering
is shown to be a characteristic property of Dirac chiral fermions in two
dimensions.Comment: final version; 4 pages, 1 eps figur
Graphene Nanoribbon and Graphene Nanodisk
We study electronic properties of graphene derivatives which have closed
edges. They are finite-length graphene nanoribbons and graphene nanodisks. No
metallic states are found in finite-length zigzag nanoribbons though all
infinite-length zigzag nanoribbons are metallic. We also study hexagonal,
parallelogrammic and trigonal nanodisks with zigzag or armchair edges. No
metallic states are found in these nanodisks either except trigonal zigzag
nanodisks. It is interesting that we can design the degeneracy of the metallic
states arbitrarily in trigonal zigzag nanodisks by changing the size.Comment: 7 pages, 5 figures, to be published in Physica E (EP2DS-17, Genova
Minimal conductivity in bilayer graphene
Using the Landauer formula approach, it is proven that minimal conductivity
of order of found experimentally in bilayer graphene is its intrinsic
property. For the case of ideal crystals, the conductivity turns our to be
equal to per valley per spin. A zero-temperature shot noise in
bilayer graphene is considered and the Fano factor is calculated. Its value
is close to the value 1/3 found earlier for the single-layer
graphene.Comment: 3 pages, 1 figur
Edge States at the Interface between Monolayer and Bilayer Graphene
The electronic property of monolayer-bilayer hybrid graphene with a zigzag
interface is studied by both the Dirac equation and numerical calculation.
There are two types of zigzag interface stacks. The dispersion and local
density of states behave quit differently along the interface at the Fermi
energy due to the different locations of the edge state. We hope our study can
give some insights in the understanding of the transport and STM experiments.Comment: 8 pages, 8 figure
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