7,962 research outputs found
Klein paradox for a pn junction in multilayer graphene
Charge carriers in single and multilayered graphene systems behave as chiral
particles due to the particular lattice symmetry of the crystal. We show that
the interplay between the meta-material properties of graphene multilayers and
the pseudospinorial properties of the charge carriers result in the occurrence
of Klein and anti-Klein tunneling for rhombohedral stacked multilayers. We
derive an algebraic formula predicting the angles at which these phenomena
occur and support this with numerical calculations for systems up to four
layers. We present a decomposition of an arbitrarily stacked multilayer into
pseudospin doublets that have the same properties as rhombohedral systems with
a lower number of layers.Comment: 5 pages, 4 figure
Hall potentiometer in the ballistic regime
We demonstrate theoretically how a two-dimensional electron gas can be used
to probe local potential profiles using the Hall effect. For small magnetic
fields, the Hall resistance is inversely proportional to the average potential
profile in the Hall cross and is independent of the shape and the position of
this profile in the junction. The bend resistance, on the other hand, is much
more sensitive on the exact details of the local potential profile in the cross
junction.Comment: 3 pages, 4 ps figure
Four band tunneling in bilayer graphene
The conductance, the transmission and the reflection probabilities through
rectangular potential barriers and pn-junctions are obtained for bilayer
graphene taking into account the four bands of the energy spectrum. We have
evaluated the importance of the skew hopping parameters {\gamma}3 and {\gamma}4
to these properties and show that for energies E>{\gamma}1/100 their effect is
negligible. For high energies two modes of propagation exist and we investigate
scattering between these modes. For perpendicular incidence both propagation
modes are decoupled and scattering between them is forbidden. This extends the
concept of pseudospin as defined within the two band approximation to a four
band model and corresponds to the (anti)symmetry of the wavefunctions under
in-plane mirroring. New transmission resonances are found that appear as sharp
peaks in the conductance which are absent in the two band approximation. The
application of an interlayer bias to the system: 1) breaks the pseudospin
structure, 2) opens a bandgap that results in a distinct feature of suppressed
transmission in the conductance, and 3) breaks the angular symmetry with
respect to normal incidence in the transmission and reflection
Few-electron eigenstates of concentric double quantum rings
Few-electron eigenstates confined in coupled concentric double quantum rings
are studied by the exact diagonalization technique. We show that the magnetic
field suppresses the tunnel coupling between the rings localizing the
single-electron states in the internal ring, and the few-electron states in the
external ring. The magnetic fields inducing the ground-state angular momentum
transitions are determined by the distribution of the electron charge between
the rings. The charge redistribution is translated into modifications of the
fractional Aharonov-Bohm period. We demonstrate that the electron distribution
can be deduced from the cusp pattern of the chemical potentials governing the
single-electron charging properties of the system. The evolution of the
electron-electron correlations to the high field limit of a classical Wigner
molecule is discussed.Comment: to appear in Physical Review
Paramagnetic adsorbates on graphene: a charge transfer analysis
We introduce a modified version of the Hirshfeld charge analysis method and
demonstrate its accurateness by calculating the charge transfer between the
paramagnetic molecule NO2 and graphene. The charge transfer between
paramagnetic molecules and a graphene layer as calculated with ab initio
methods can crucially depend on the size of the supercell used in the
calculation. This has important consequences for adsorption studies involving
paramagnetic molecules such as NO2 physisorbed on graphene or on carbon
nanotubes.Comment: 4 pages, 4 figures, submitted to Applied Physics Letter
Violation of Onsager symmetry for a ballistic channel Coulomb coupled to a quantum ring
We investigate a scattering of electron which is injected individually into
an empty ballistic channel containing a cavity that is Coulomb coupled to a
quantum ring charged with a single-electron.
We solve the time-dependent Schr\"odinger equation for the electron pair with
an exact account for the electron-electron correlation. Absorption of energy
and angular momentum by the quantum ring is not an even function of the
external magnetic field. As a consequence we find that the electron
backscattering probability is asymmetric in the magnetic field and thus
violates Onsager symmetry.Comment: submitted to EP
Graphene: a perfect nanoballoon
We have performed a first-principles density functional theory investigation
of the penetration of helium atoms through a graphene monolayer with defects.
The relaxation of the graphene layer caused by the incoming helium atoms does
not have a strong influence on the height of the energy barriers for
penetration. For defective graphene layers, the penetration barriers decrease
exponentially with the size of the defects but they are still sufficiently high
that very large defects are needed to make the graphene sheet permeable for
small atoms and molecules. This makes graphene a very promising material for
the construction of nanocages and nanomembranes.Comment: 4 pages, 4 figures, submitted to Applied Physics Letter
Double quantum dots defined in bilayer graphene
Artificial molecular states of double quantum dots defined in bilayer
graphene are studied with the atomistic tight-binding and its low-energy
continuum approximation. We indicate that the extended electron wave functions
have opposite parities on each of the sublattices at both graphene layers and
that the ground-state wave function components change from bonding to
antibonding with the interdot distance. In the weak coupling limit -- the most
relevant for the quantum dots defined electrostatically -- the signatures of
the interdot coupling include -- for the two-electron ground state -- formation
of states with symmetric or antisymmetric spatial wave functions split by the
exchange energy. In the high energy part of the spectrum the states with both
electrons in the same dot are found with the splitting of energy levels
corresponding to simultaneous tunneling of the electron pair from one dot to
the other
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