23,302 research outputs found
Strong mobility degradation in ideal graphene nanoribbons due to phonon scattering
We investigate the low-field phonon-limited mobility in armchair graphene
nanoribbons (GNRs) using full-band electron and phonon dispersion relations. We
show that lateral confinement suppresses the intrinsic mobility of GNRs to
values typical of common bulk semiconductors, and very far from the impressive
experiments on 2D graphene. Suspended GNRs with a width of 1 nm exhibit a
mobility close to 500 cm^2/Vs at room temperature, whereas if the same GNRs are
deposited on HfO2 mobility is further reduced to about 60 cm^2/Vs due to
surface phonons. We also show the occurrence of polaron formation, leading to
band gap renormalization of ~118 meV for 1 nm-wide armchair GNRs.Comment: 11 pages, 4 figure
Chirality Selection in Open Flow Systems and in Polymerization
As an attempt to understand the homochirality of organic molecules in life, a
chemical reaction model is proposed where the production of chiral monomers
from achiral substrate is catalyzed by the polymers of the same enatiomeric
type. This system has to be open because in a closed system the enhanced
production of chiral monomers by enzymes is compensated by the associated
enhancement in back reaction, and the chiral symmetry is conserved. Open flow
without cross inhibition is shown to lead to the chirality selection in a
general model. In polymerization, the influx of substrate from the ambience and
the efflux of chiral products for purposes other than the catalyst production
make the system necessarily open. The chiral symmetry is found to be broken if
the influx of substrate lies within a finite interval. As the efficiency of the
enzyme increases, the maximum value of the enantiomeric excess approaches unity
so that the chirality selection becomes complete.Comment: 8 pages, 4 figure
Finite-dimensional analogs of string s <-> t duality and pentagon equation
We put forward one of the forms of functional pentagon equation (FPE), known
from the theory of integrable models, as an algebraic explanation to the
phenomenon known in physics as st duality. We present two simple geometrical
examples of FPE solutions, one of them yielding in a particular case the
well-known Veneziano expression for 4-particle amplitude. Finally, we interpret
our solutions of FPE in terms of relations in Lie groups.Comment: LaTeX, 12 pages, 6 eps figure
In-medium electron-nucleon scattering
In-medium nucleon electromagnetic form factors are calculated in the quark
meson coupling model. The form factors are typically found to be suppressed as
the density increases. For example, at normal nuclear density and , the nucleon electric form factors are reduced by approximately 8%
while the magnetic form factors are reduced by only 1 - 2%. These variations
are consistent with current experimental limits but should be tested by more
precise experiments in the near future.Comment: 14 pages, latex, 3 figure
Neutral triplet Collective Mode as a new decay channel in Graphite
In an earlier work we predicted the existence of a neutral triplet collective
mode in undoped graphene and graphite [Phys. Rev. Lett. {\bf 89} (2002) 16402].
In this work we study a phenomenological Hamiltonian describing the interaction
of tight-binding electrons on honeycomb lattice with such a dispersive neutral
triplet boson. Our Hamiltonian is a generalization of the Holstein polaron
problem to the case of triplet bosons with non-trivial dispersion all over the
Brillouin zone. This collective mode constitutes an important excitation branch
which can contribute to the decay rate of the electronic excitations. The
presence of such collective mode, modifies the spectral properties of electrons
in graphite and undoped graphene. In particular such collective mode, as will
be shown in this paper, can account for some part of the missing decay rate in
a time-domain measurement done on graphite
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
Intersubband Edge Singularity in Metallic Nanotubes
Tunneling density of states of both the massless and massive (gapped)
particles in metallic carbon nanotubes is known to have anomalous energy
dependence. This is the result of coupling to multiple low-energy bosonic
excitation (plasmons). For both kinds of particles the ensuing effect is the
suppression of the density of states by electron-electron interactions. We
demonstrate that the optical absorption between gapless and gapped states is
affected by the many-body effects in the opposite way. The absorption
probability is enhanced compared with the non-interacting value and develops a
power-law frequency dependence with the exponent -0.2 for typical nanotubes.Comment: 4 pages, 1 figure (final version, discussion of Sommerfeld factor and
Ref. 11 added
Magnetodielectric Response of the Spin-Ice Dy2Ti2O7
We report the magneto-dielectric response of single crystals of the spin-ice
compound Dy2Ti2O7 down to 0.26 K. The dielectric constant under zero magnetic
field exhibits a clear decrease reflecting the development of the local
two-spins-in, two-spins-out structure below about 1.2 K. Both the real and
imaginary parts of the dielectric constant under magnetic fields sensitively
respond to various changes in the spin structures. We found that the real part
can be described in terms of local spin correlations among the moments of
tetrahedra, rather than among individual Dy3+ moments. Using the peaks in the
imaginary part, we have constructed a precise field-temperature phase diagram
in the [111] field direction. We thus demonstrate that the magneto-dielectric
response can be a high-sensitivity local probe of the spin state of
geometrically frustrated systems.Comment: 6 pages, 6 figure
Self-consistent quantum effects in the quark meson coupling model
We derive the equation of state of nuclear matter including vacuum
polarization effects arising from the nucleons and the sigma mesons in the
quark-meson coupling model which incorporates explicitly quark degrees of
freedom with quark coupled to the scalar and vector mesons. This leads to a
softer equation of state for nuclear matter giving a lower value of
incompressibility than would be reached without quantum effects. The {\it
in-medium} nucleon and sigma meson masses are also calculated in a
self-consistent manner.Comment: 10 pages, latex, 5 figure
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