23,273 research outputs found
Case of Almost Redundant Components in 3 alpha Faddeev Equations
The 3 alpha orthogonality condition model using the Pauli-forbidden bound
states of the Buck, Friedlich and Wheatly alpha alpha potential can yield a
compact 3 alpha ground state with a large binding energy, in which a small
admixture of the redundant components can never be eliminated.Comment: Revtex V4.0, 4 pages, no figure
Magnetization of a half-quantum vortex in a spinor Bose-Einstein condensate
Magnetization dynamics of a half-quantum vortex in a spin-1 Bose-Einstein
condensate with a ferromagnetic interaction are investigated by mean-field and
Bogoliubov analyses. The transverse magnetization is shown to break the
axisymmetry and form threefold domains. This phenomenon originates from the
topological structure of the half-quantum vortex and spin conservation.Comment: 6 pages, 3 figure
Disorder-induced double resonant Raman process in graphene
An analytical study is presented of the double resonant Raman scattering
process in graphene, responsible for the D and D features in the
Raman spectra. This work yields analytical expressions for the D and
D integrated Raman intensities that explicitly show the dependencies
on laser energy, defect concentration, and electronic lifetime. Good agreement
is obtained between the analytical results and experimental measurements on
samples with increasing defect concentrations and at various laser excitation
energies. The use of Raman spectroscopy to identify the nature of defects is
discussed. Comparison between the models for the edge-induced and the
disorder-induced D band intensity suggests that edges or grain boundaries can
be distinguished from disorder by the different dependence of their Raman
intensity on laser excitation energy. Similarly, the type of disorder can
potentially be identified not only by the intensity ratio
, but also by its laser energy
dependence. Also discussed is a quantitative analysis of quantum interference
effects of the graphene wavefunctions, which determine the most important
phonon wavevectors and scattering processes responsible for the D and
D bands.Comment: 10 pages, 4 figure
Enhanced dispersion interaction between quasi-one dimensional conducting collinear structures
Recent investigations have highlighted the failure of a sum of terms
to represent the dispersion interaction in parallel metallic, anisotropic,
linear or planar nanostructures [J. F. Dobson, A. White, and A. Rubio, Phys.
Rev. Lett. 96, 073201 (2006) and references therein]. By applying a simple
coupled plasmon approach and using electron hydrodynamics, we numerically
evaluate the dispersion (non-contact van der Waals) interaction between two
conducting wires in a collinear pointing configuration. This case is compared
to that of two insulating wires in an identical geometry, where the dispersion
interaction is modelled both within a pairwise summation framework, and by
adding a pinning potential to our theory leading to a standard oscillator-type
model of insulating dielectric behavior. Our results provide a further example
of enhanced dispersion interaction between two conducting nanosystems compared
to the case of two insulating ones. Unlike our previous work, this calculation
explores a region of relatively close coupling where, although the electronic
clouds do not overlap, we are still far from the asymptotic region where a
single power law describes the dispersion energy. We find that strong
differences in dispersion attraction between metallic and semiconducting /
insulating cases persist into this non-asymptotic region. While our theory will
need to be supplemented with additional short-ranged terms when the electronic
clouds overlap, it does not suffer from the short-distance divergence exhibited
by purely asymptotic theories, and gives a natural saturation of the dispersion
energy as the wires come into contact.Comment: 10 pages, 5 figures. Added new extended numerical calculations, new
figures, extra references and heavily revised tex
Energy Anomaly and Polarizability of Carbon Nanotubes
The energy of electron Fermi sea perturbed by external potential, represented
as energy anomaly which accounts for the contribution of the deep-lying states,
is analyzed for massive d = 1+1 Dirac fermions on a circle. The anomaly is a
universal function of the applied field, and is related to known
field-theoretic anomalies. We express transverse polarizability of Carbon
nanotubes via the anomaly, in a way which exhibits the universality and
scale-invariance of the response dominated by pi-electrons and qualitatively
different from that of dielectric and conducting shells. Electron band
transformation in a strong-field effect regime is predicted.Comment: 4 pg
Quark-Meson Coupling Model for a Nucleon
The quark-meson coupling model for a nucleon is considered. The model
describes a nucleon as an MIT bag, in which quarks are coupled to scalar and
vector mesons. A set of coupled equations for the quark and the meson fields
are obtained and are solved in a self-consistent way. It is shown that the mass
of a nucleon as a dressed MIT bag interacting with sigma- and omega-meson
fields significantly differs from the mass of a free MIT bag. A few sets of
model parameters are obtained so that the mass of a dressed MIT bag becomes the
nucleon mass. The results of our calculations imply that the self-energy of the
bag in the quark-meson coupling model is significant and needs to be considered
in doing the nuclear matter calculations.Comment: 3 figure
Microscopic energy flows in disordered Ising spin systems
An efficient microcanonical dynamics has been recently introduced for Ising
spin models embedded in a generic connected graph even in the presence of
disorder i.e. with the spin couplings chosen from a random distribution. Such a
dynamics allows a coherent definition of local temperatures also when open
boundaries are coupled to thermostats, imposing an energy flow. Within this
framework, here we introduce a consistent definition for local energy currents
and we study their dependence on the disorder. In the linear response regime,
when the global gradient between thermostats is small, we also define local
conductivities following a Fourier dicretized picture. Then, we work out a
linearized "mean-field approximation", where local conductivities are supposed
to depend on local couplings and temperatures only. We compare the approximated
currents with the exact results of the nonlinear system, showing the
reliability range of the mean-field approach, which proves very good at high
temperatures and not so efficient in the critical region. In the numerical
studies we focus on the disordered cylinder but our results could be extended
to an arbitrary, disordered spin model on a generic discrete structures.Comment: 12 pages, 6 figure
Variations of Hadron Masses and Matter Properties in Dense Nuclear Matter
Using a self-consistent quark model for nuclear matter we investigate
variations of the masses of the non-strange vector mesons, the hyperons and the
nucleon in dense nuclear matter (up to four times the normal nuclear density).
We find that the changes in the hadron masses can be described in terms of the
value of the scalar mean-field in matter. The model is then used to calculate
the density dependence of the quark condensate in-medium, which turns out to be
well approximated by a linear function of the nuclear density. Some relations
among the hadron properties and the in-medium quark condensate are discussed.Comment: 22 pages, University of Adelaide preperint ADP-94-20/T160, submitted
to Physical Review
Lifshitz-type formulas for graphene and single-wall carbon nanotubes: van der Waals and Casimir interations
Lifshitz-type formulas are obtained for the van der Waals and Casimir
interaction between graphene and a material plate, graphene and an atom or a
molecule, and between a single-wall carbon nanotube and a plate. The reflection
properties of electromagnetic oscillations on graphene are governed by the
specific boundary conditions imposed on the infinitely thin positively charged
plasma sheet, carrying a continuous fluid with some mass and charge density.
The obtained formulas are applied to graphene interacting with Au and Si
plates, to hydrogen atoms and molecules interacting with graphene, and to
single-wall carbon nanotubes interacting with Au and Si plates. The
generalizations to more complicated carbon nanostructures are discussed.Comment: 11 pages, 5 figures, 2 tables; to appear in Phys. Rev. B; misprints
in Eqs.(33) and (34) are correcte
AC transport in graphene-based Fabry-Perot devices
We report on a theoretical study of the effects of time-dependent fields on
electronic transport through graphene nanoribbon devices. The Fabry-P\'{e}rot
interference pattern is modified by an ac gating in a way that depends strongly
on the shape of the graphene edges. While for armchair edges the patterns are
found to be regular and can be controlled very efficiently by tuning the ac
field, samples with zigzag edges exhibit a much more complex interference
pattern due to their peculiar electronic structure. These studies highlight the
main role played by geometric details of graphene nanoribbons within the
coherent transport regime. We also extend our analysis to noise power response,
identifying under which conditions it is possible to minimize the current
fluctuations as well as exploring scaling properties of noise with length and
width of the systems
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