12,583 research outputs found
Coulomb blockade in graphene nanoribbons
We propose that recent transport experiments revealing the existence of an
energy gap in graphene nanoribbons may be understood in terms of Coulomb
blockade. Electron interactions play a decisive role at the quantum dots which
form due to the presence of necks arising from the roughness of the graphene
edge. With the average transmission as the only fitting parameter, our theory
shows good agreement with the experimental data.Comment: 4 pages, 2 figure
Negative Hopping Magnetoresistance and Dimensional Crossover in Lightly Doped Cuprate Superconductors
We show that, due to the weak ferromagnetism of LaSrCuO, an
external magnetic field leads to a dimensional crossover 2D 3D for the
in-plane transport. The crossover results in an increase of the hole's
localization length and hence in a dramatic negative magnetoresistance in the
variable range hopping regime. This mechanism quantitatively explains puzzling
experimental data on the negative magnetoresistance in the N\'eel phase of
LaSrCuO.Comment: 6 pages, 3 figures; published versio
The photino sector and a confining potential in a supersymetric Lorentz-symmetry-violating model
We study the spectrum of the minimal supersymmetric extension of the
Carroll-Field-Jackiw model for Electrodynamics with a topological
Chern-Simons-like Lorentz-symmetry violating term. We identify a number of
independent background fermion condensates, work out the gaugino dispersion
relation and propose a photonic effective action to consider aspects of
confinement induced by the SUSY background fermion condensates, which also
appear to signal Lorentz-symmetry violation in the photino sector of the
action. Our calculations of the static potential are carried out within the
framework of the gauge-invariant but path-dependent variables formalism which
are alternative to the Wilson loop approach. Our results show that the
interaction energy contains a linear term leading to the confinement of static
probe charges.Comment: 11 pages, photino dispersion relation is extended to included the
case the photino acquires mass through spontaneous SUSY breakin
Aspects of CPT-even Lorentz-symmetry violating physics in a supersymmetric scenario
Background fermion condensates in a landscape dominated by global SUSY are
reassessed in connection with a scenario where Lorentz symmetry is violated in
the bosonic sector (actually, the photon sector) by a -even -term. An
effective photonic action is discussed that originates from the supersymmetric
background fermion condensates. Also, the photino mass emerges in terms of a
particular condensate contrary to what happens in the -violation.
Finally, the interparticle potential induced by the effective photonic action
is investigated and a confining profile is identified.Comment: 14 pages. arXiv admin note: text overlap with arXiv:1102.3777 by
other author
A 3-form Gauge Potential in 5D in connection with a Possible Dark Sector of 4D-Electrodynamics
We here propose a 5-dimensional {\bf Abelian gauge} model based on the mixing
between a potential and an Abelian 3-form field by means of a
topological mass term. An extended covariant derivative is introduced to
minimally couple a Dirac field to the potential, while this same
covariant derivative non-minimally couples the 3-form field to the charged
fermion. A number of properties are discussed in 5D; in particular, the
appearance of a topological fermionic current. A 4-dimensional reduced version
of the model is investigated and, { \bf in addition to the electric- and
magnetic-sort of fields,} there emerges an extra set of electric- and
magnetic-like fields which contribute a negative pressure and may be identified
as a possible fraction of dark energy. The role of the topological fermionic
current is also contemplated upon dimensional reduction from 5D to 4D. Other
issues we present in 4 space-time dimensions are the emergence {\bf of a
pseudo-scalar massive particle,} an extra massive neutral gauge boson,{\bf
which we interpret as a kind of paraphoton}, and the calculation of spin- and
velocity-dependent interparticle potentials associated to the exchange of the
intermediate bosonic fields of the model.Comment: -- 30 pages -- L. P. R. Ospedal appears as a new co-author;
modifications by inclusion of the gravitational sector and the attainment of
a spin- and velocity-dependent potential as an application have been worked
out in this Revised Versio
A modified proximity approach in the fusion of heavy-ions
By using a suitable set of the surface energy coefficient, nuclear radius,
and universal function, the original proximity potential 1977 is modified. The
overestimate of the data by 4 % reported in the literature is significantly
reduced. Our modified proximity potential reproduces the experimental data
nicely compared to its older versions.Comment: 9 pages, 5 figures, Chin. Phys. lett.(2010) in pres
One-magnon Raman scattering in La(2)CuO(4): the origin of the field-induced mode
We investigate the one-magnon Raman scattering in the layered
antiferromagnetic La(2)CuO(4) compound. We find that the Raman signal is
composed by two one-magnon peaks: one in the B1g channel, corresponding to the
Dzyaloshinskii-Moryia (DM) mode, and another in the B3g channel, corresponding
to the XY mode. Furthermore, we show that a peak corresponding to the XY mode
can be induced in the planar (RR) geometry when a magnetic field is applied
along the easy axis for the sublattice magnetization. The appearance of such
field-induced mode (FIM) signals the existence of a new magnetic state above
the Neel temperature T_N, where the direction of the weak-ferromagnetic moment
(WFM) lies within the CuO(2) planes.Comment: 4 pages, 3 figure
Sistema portátil de fluorescência induzida por laser para análise de matéria orgânica em solos.
Quantum Cosmology in Scalar-Tensor Theories With Non Minimal Coupling
Quantization in the minisuperspace of non minimal scalar-tensor theories
leads to a partial differential equation which is non separable. Through a
conformal transformation we can recast the Wheeler-DeWitt equation in an
integrable form, which corresponds to the minimal coupling case, whose general
solution is known. Performing the inverse conformal transformation in the
solution so found, we can construct the corresponding one in the original
frame. This procedure can also be employed with the bohmian trajectories. In
this way, we can study the classical limit of some solutions of this quantum
model. While the classical limit of these solutions occurs for small scale
factors in the Einstein's frame, it happens for small values of the scalar
field non minimally coupled to gravity in the Jordan's frame, which includes
large scale factors.Comment: latex, 18 page
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