12,250 research outputs found
Identification of fullerene-like CdSe nanoparticles from optical spectroscopy calculations
Semiconducting nanoparticles are the building blocks of optical nanodevices
as their electronic states, and therefore light absorption and emission, can be
controlled by modifying their size and shape. CdSe is perhaps the most studied
of these nanoparticles, due to the efficiency of its synthesis, the high
quality of the resulting samples, and the fact that the optical gap is in the
visible range. In this article, we study light absorption of CdSe
nanostructures with sizes up to 1.5 nm within density functional theory. We
study both bulk fragments with wurtzite symmetry and novel fullerene-like
core-cage structures. The comparison with recent experimental optical spectra
allows us to confirm the synthesis of these fullerene-like CdSe clusters
Generalized scalar field models with the same energy density and linear stability
We study how the properties of a Lagrangian density for a single real scalar
field in flat spacetime change with inclusion of an overall factor depending
only on the field. The focus of the paper is to obtain analytical results. So,
we show that even though it is possible to perform a field redefinition to get
an equivalent canonical model, it is not always feasible to write the canonical
model in terms of elementary functions. Also, we investigate the behavior of
the energy density and the linear stability of the solutions. Finally, we show
that one can find a class of models that present the same energy density and
the same stability potential.Comment: 6 pages, 4 figure
Time and energy-resolved two photon-photoemission of the Cu(100) and Cu(111) metal surfaces
We present calculations on energy- and time-resolved two-photon photoemission
spectra of images states in Cu(100) and Cu(111) surfaces. The surface is
modeled by a 1D effective potential and the states are propagated within a
real-space, real-time method. To obtain the energy resolved spectra we employ a
geometrical approach based on a subdivision of space into two regions. We treat
electronic inelastic effects by taking into account the scattering rates
calculated within a GW scheme. To get further insight into the decaying
mechanism we have also studied the effect of the variation of the classical
Hartree potential during the excitation. This effect turns out to be small.Comment: 11 pages, 7 figure
Analytic vortex solutions in generalized models of the Maxwell-Higgs type
This work deals with the presence of analytical vortex configurations in
generalized models of the Maxwell-Higgs type in the three-dimensional
spacetime. We implement a procedure that allows to decouple the first order
equations, which we use to solve the model analytically. The approach is
exemplified with three distinct models that show the robustness of the
construction. In the third model, one finds analytical solutions that exhibit
interesting compact vortex behavior.Comment: 9 pages, 10 figures. To appear in PL
Compact Structures in Standard Field Theory
We investigate the presence of static solutions in models described by real
scalar field in two-dimensional spacetime. After taking advantage of a
procedure introduced sometime ago, we solve intricate nonlinear ordinary
differential equations and illustrate how to find compact structures in models
engendering standard kinematics. In particular, we study linear stability and
show that all the static solutions we have found are linearly stable.Comment: 6 pages, 11 figures; version published in EP
From Kinks to Compactons
This work deals with the presence of localized structures in relativistic
systems described by a single real scalar field in two-dimensional spacetime.
We concentrate on kinks and compactons in models with standard kinematics, and
we develop a procedure that help us to smoothly go from kinks to compactons in
the suggested scenario. We also show how the procedure works in the braneworld
scenario, for flat brane in the five-dimensional spacetime with a single extra
dimension of infinite extent. The brane unveils a hybrid profile when the kink
becomes a compacton, behaving as a thick or thin brane, depending on the extra
dimension being inside or outside a compact space.Comment: 7 pages, 7 figures; new version, to appear in PL
Vortices in a generalized Maxwell-Higgs model with visible and hidden sectors
We investigate the presence of vortices in generalized Maxwell-Higgs models
with a hidden sector. The model engenders symmetry, in a
manner that the sectors are coupled via the visible magnetic permeability
depending only on the hidden scalar field. We develop a first order framework
in which the hidden sector decouples from the visible one. We illustrate the
results with two specific examples, that give rise to the presence of vortices
with internal structure.Comment: 9 two-column pages, 4 figures; version to appear in AHE
Excitonic effects in the optical properties of CdSe nanowires
Using a first-principle approach beyond density functional theory we
calculate the electronic and optical properties of small diameter CdSe
nanowires.Our results demonstrate how some approximations commonly used in bulk
systems fail at this nano-scale level and how indispensable it is to include
crystal local fields and excitonic effects to predict the unique optical
properties of nanowires. From our results, we then construct a simple model
that describes the optical gap as a function of the diameter of the wire, that
turns out to be in excellent agreement with experiments for intermediate and
large diameters.Comment: submitte
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