22,536 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
Spectra of primordial fluctuations in two-perfect-fluid regular bounces
We introduce analytic solutions for a class of two components bouncing
models, where the bounce is triggered by a negative energy density perfect
fluid. The equation of state of the two components are constant in time, but
otherwise unrelated. By numerically integrating regular equations for scalar
cosmological perturbations, we find that the (would be) growing mode of the
Newtonian potential before the bounce never matches with the the growing mode
in the expanding stage. For the particular case of a negative energy density
component with a stiff equation of state we give a detailed analytic study,
which is in complete agreement with the numerical results. We also perform
analytic and numerical calculations for long wavelength tensor perturbations,
obtaining that, in most cases of interest, the tensor spectral index is
independent of the negative energy fluid and given by the spectral index of the
growing mode in the contracting stage. We compare our results with previous
investigations in the literature.Comment: 11 pages, 5 figure
Charged branes interactions via Kalb-Ramond field
Because of its versatility, the 2-form field has been employed to describe a
multitude of scenarios that range from high energy to condensed matter physics.
Pushing forward in this endeavor we study the interaction energy, intermediated
by this kind of field, between branes in a variety of configurations. Also, the
so-called Cremmer-Scherk-Kalb-Ramond model, which consists of the
electromagnetic field coupled to the Kalb-Ramond gauge potential, is
considered. It turns out that these models exhibit a much richer class of
sources than usually thought, able to intermediate novel forms of interactions
in different scenarios.Comment: 12 latex pages, more general result
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