98 research outputs found
Gate induced enhancement of spin-orbit coupling in dilute fluorinated graphene
We analyze the origin of spin-orbit coupling (SOC) in fluorinated graphene
using Density Functional Theory (DFT) and a tight-binding model for the
relevant orbitals. As it turns out, the dominant source of SOC is the atomic
spin-orbit of fluorine adatoms and not the impurity induced SOC based on the
distortion of the graphene plane as in hydrogenated graphene. More
interestingly, our DFT calculations show that SOC is strongly affected by both
the type and concentrations of the graphene's carriers, being enhanced by
electron doping and reduced by hole doping. This effect is due to the charge
transfer to the fluorine adatom and the consequent change in the
fluorine-carbon bonding. Our simple tight-binding model, that includes the SOC
of the orbitals of F and effective parameters based on maximally localized
Wannier functions, is able to account for the effect. The strong enhancement of
the SOC induced by graphene doping opens the possibility to tune the spin
relaxation in this material.Comment: 9 pages, 8 figure
Diffusion of fluorine adatoms on doped graphene
We calculate the diffusion barrier of fluorine adatoms on doped graphene in
the diluted limit using Density Functional Theory. We found that the barrier
strongly depends on the magnitude and character of the graphene's
doping (): it increases for hole doping () and decreases
for electron doping (). Near the neutrality point the functional
dependence can be approximately by where
meVcm. This effect leads to significant
changes of the diffusion constant with doping even at room temperature and
could also affect the low temperature diffusion dynamics due to the presence of
substrate induced charge puddles. In addition, this might open up the
possibility to engineer the F dynamics on graphene by using local gates.Comment: 4 pages, 4 figure
Study of the leptonic decays of pseudoscalar and vector mesons and of the semileptonic and decays
We present results for different observables in weak decays of pseudoscalar
and vector mesons with a heavy or quark. The calculations are done in a
nonrelativistic constituent quark model improved at some instances by heavy
quark effective theory constraints. We determine pseudoscalar and vector meson
decay constants that within a few per cent satisfy , a
result expected in heavy quark symmetry when the heavy quark masses tend to
infinity. We also analyze the semileptonic and decays for
which we evaluate the different form factors. Here we impose heavy quark
effective theory constraints among form factors that are not satisfied by a
direct quark model calculation. The value of the form factors at zero recoil
allows us to determine, by comparison with experimental data, the value of the
Cabbibo-Kobayashi-Maskawa matrix element. From the
semileptonic decay we get in perfect agreement with
our previous determination based on the study of the semileptonic decay and also in excellent agreement with a recent experimental
determination by the DELPHI Collaboration. We further make use of the partial
conservation of axial current hypothesis to determine the strong coupling
constants and . The
ratio agrees with the heavy quark symmetry
prediction of 1.Comment: 19 Latex pages,6 figures, references added, corrected typos, content
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On the components of the unstable set of isolated invariant sets
The aim of this note is to shed some light on the topological structure of the unstable set of an isolated invariant set K. We give a bound on the number of essential quasicomponents of the unstable set of K in terms of the homological Conley index of K. The proof relies on an explicit pairing between Čech homology classes and Alexander–Spanier cohomology classes that takes the form of an integral.Depto. de Álgebra, Geometría y TopologíaFac. de Ciencias MatemáticasTRUEMinisterio de Ciencia, Innovación y Universidadespu
¿Fotografiamos el color tal y como lo percibimos?
Pretendemos en este trabajo que nuestros alumnos conozcan algunos aspectos de nuestro sistema visual, en concreto aquellos referidos a la visión del color, usando para ello un dispositivo tan familiar y tan común como su propia cámara digital.Palabras clave: color; reflectancia; iluminante; balance de blanco.Do we really take pictures of colors as we perceive them?We intend in this work that our students know some aspects of our visual system, specifically those related to color vision, that can use it as something familiar and as common as their own digital camera.Keywords: color; reflectance; illuminant; white balance
Study of the strong , and decays in a nonrelativistic quark model
We present results for the strong widths corresponding to the , and
decays. The calculations have been done in a nonrelativistic constituent quark
model with wave functions that take advantage of the constraints imposed by
heavy quark symmetry. Partial conservation of axial current hypothesis allows
us to determine the strong vertices from an analysis of the axial current
matrix elements. Our results \hbox{}, {}, {}, {}, {},
{}, {} and {} are in good
agreement with experimental determinations.Comment: 8 latex pages. Shortened version accepted for publication in Physical
Review
Study of exclusive semileptonic and nonleptonic decays of B-c(-) in a nonrelativistic quark model
We present results for different observables measured in semileptonic and nonleptonic decays of the B-c(-) meson. The calculations have been done within the framework of a nonrelativistic constituent quark model. In order to check the sensitivity of all our results against the interquark interaction we use five different quark-quark potentials. We obtain form factors, decay widths, and asymmetry parameters for semileptonic B-c(-)-> c (c) over bar and B-c(-)->(B) over bar decays. In the limit of infinite heavy quark mass, our model reproduces the constraints of heavy quark spin symmetry. For the actual heavy quark masses we find nonetheless large corrections to that limiting situation for some form factors. We also analyze exclusive nonleptonic two-meson decay channels within the factorization approximation
Fermion contribution to the static quantities of arbitrarily charged vector bosons
We present an analysis of the one-loop contribution from left- and
right-handed fermions to the static electromagnetic properties of an
arbitrarily charged no self-conjugate vector boson . Particular emphasis is
given to the case of a no self-conjugate neutral boson . Regardless the
electric charge of the boson, a fermionic loop can induce the two CP-even
form factors but only one CP-odd. As a result the corresponding electric dipole
moment is directly proportional to the magnetic quadrupole moment. The CP-odd
form factor might be severely suppressed since it requires the presence of both
left- and right-handed fermions. The behavior of the form factors is analyzed
for several scenarios of the fermion masses in the context of the decoupling
theorem.Comment: 12 pages, 3 figures, submitted to Journal of Physics
The two pion decay of the Roper resonance
We evaluate the two pion decay of the Roper resonance in a model where
explicit re-scattering of the two final pions is accounted for by the use of
unitarized chiral perturbation theory. Our model does not include an explicit
or scalar-isoscalar meson decay mode, instead it
generates it dynamically by means of the pion re-scattering. The two ways,
explicit or dynamically generated, of introducing this decay channel have very
different amplitudes.
Nevertheless, through interference with the other terms of the model we are
able to reproduce the same phenomenology as models with explicit consideration
of the meson.Comment: 17 latex pages, 11 eps figures. A few misprints corrected. A few new
references. Version accepted for publication in Phys. Rev.
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