919 research outputs found
Snake states in graphene quantum dots in the presence of a p-n junction
We investigate the magnetic interface states of graphene quantum dots that
contain p-n junctions. Within a tight-binding approach, we consider rectangular
quantum dots in the presence of a perpendicular magnetic field containing p-n,
as well as p-n-p and n-p-n junctions. The results show the interplay between
the edge states associated with the zigzag terminations of the sample and the
snake states that arise at the p-n junction, due to the overlap between
electron and hole states at the potential interface. Remarkable localized
states are found at the crossing of the p-n junction with the zigzag edge
having a dumb-bell shaped electron distribution. The results are presented as
function of the junction parameters and the applied magnetic flux.Comment: 13 pages, 23 figures, to be appeared in Phys. Rev.
Simplified model for the energy levels of quantum rings in single layer and bilayer graphene
Within a minimal model, we present analytical expressions for the eigenstates
and eigenvalues of carriers confined in quantum rings in monolayer and bilayer
graphene. The calculations were performed in the context of the continuum
model, by solving the Dirac equation for a zero width ring geometry, i.e. by
freezing out the carrier radial motion. We include the effect of an external
magnetic field and show the appearance of Aharonov-Bohm oscillations and of a
non-zero gap in the spectrum. Our minimal model gives insight in the energy
spectrum of graphene-based quantum rings and models different aspects of finite
width rings.Comment: To appear in Phys. Rev.
Topological confinement in graphene bilayer quantum rings
We demonstrate the existence of localized electron and hole states in a
ring-shaped potential kink in biased bilayer graphene. Within the continuum
description, we show that for sharp potential steps the Dirac equation
describing carrier states close to the K (or K') point of the first Brillouin
zone can be solved analytically for a circular kink/anti-kink dot. The
solutions exhibit interfacial states which exhibit Aharonov-Bohm oscillations
as functions of the height of the potential step and/or the radius of the ring
Conditions for non-monotonic vortex interaction in two-band superconductors
We describe a semi-analytic approach to the two-band Ginzburg-Landau theory,
which predicts the behavior of vortices in two-band superconductors. We show
that the character of the short-range vortex-vortex interaction is determined
by the sign of the normal domain - superconductor interface energy, in analogy
with the conventional differentiation between type-I and type-II
superconductors. However, we also show that the long-range interaction is
determined by a modified Ginzburg-Landau parameter , different from
the standard of a bulk superconductor. This opens the possibility for
non-monotonic vortex-vortex interaction, which is temperature-dependent, and
can be further tuned by alterations of the material on the microscopic scale
New Records Of Aparasphenodon Bokermanni (pombal, 1993) From Santa Catarina, Southern Brazil, And Extension Of Genus Range (anura: Hylidae)
Aparasphenodon bokermanni is a poorly known casque-headed tree frog found in São Paulo and Santa Catarina, southern Brazil. Here we provide two new records, one from Joinville, northeastern Santa Catarina, and the first record from Santa Catarina Island, Brazil, which extends to the south the range of the genus by approximately 150 km. © 2016 Check List and Authors.12
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