7,224 research outputs found
X-Ray Reflectivity of Fibonacci Multilayers
We have numerically computed the reflectivity of X-ray incident normally onto
Fibonacci multilayers, and compared the results with those obtained in periodic
approximant multilayers. The constituent layers are of low and high refractive
indices with the same thickness. Whereas reflectivity of periodic approximant
multilayers changes only slightly with increasing the number of layers,
Fibonacci multilayers present a completely different behaviour. In particular,
we have found a highly-fragmented and self-similar reflectivity pattern in
Fibonacci systems. The behaviour of the fragmentation pattern on increasing the
number of layers is quantitatively described using multifractal techniques. The
paper ends with a brief discussion on possible practical applications of our
results in the design of new X-ray devices.Comment: 8 pages, REVTeX 3.0, 3 figures available upon request from
[email protected]. To appear in Physics Letters
Frenkel Excitons in Random Systems With Correlated Gaussian Disorder
Optical absorption spectra of Frenkel excitons in random one-dimensional
systems are presented. Two models of inhomogeneous broadening, arising from a
Gaussian distribution of on-site energies, are considered. In one case the
on-site energies are uncorrelated variables whereas in the second model the
on-site energies are pairwise correlated (dimers). We observe a red shift and a
broadening of the absorption line on increasing the width of the Gaussian
distribution. In the two cases we find that the shift is the same, within our
numerical accuracy, whereas the broadening is larger when dimers are
introduced. The increase of the width of the Gaussian distribution leads to
larger differences between uncorrelated and correlated disordered models. We
suggest that this higher broadening is due to stronger scattering effects from
dimers.Comment: 9 pages, REVTeX 3.0, 3 ps figures. To appear in Physical Review
Feshbach-type resonances for two-particle scattering in graphene
Two-particle scattering in graphene is a multichannel problem, where the
energies of the identical or opposite-helicity channels lie in disjoint energy
segments. Due to the absence of Galilean invariance, these segments depend on
the total momentum . The dispersion relations for the two opposite-helicity
scattering channels are analogous to those of two one-dimensional tight-binding
lattices with opposite dispersion relations, which are known to easily bind
states at their edges. When an -wave separable interaction potential is
assumed, those bound states reveal themselves as three Feshbach resonances in
the identical-helicity channel. In the limit , one of the
resonances survives and the opposite-helicity scattering amplitudes vanish.Comment: 8 pages, 2 figure
Attractions between charged colloids at water interfaces
The effective potential between charged colloids trapped at water interfaces
is analyzed. It consists of a repulsive electrostatic and an attractive
capillary part which asymptotically both show dipole--like behavior. For
sufficiently large colloid charges, the capillary attraction dominates at large
separations.
The total effective potential exhibits a minimum at intermediate separations
if the Debye screening length of water and the colloid radius are of comparable
size.Comment: 8 pages, 1 figure, revised version (one paragraph added) accepted in
JPC
Nonequilibrium critical dynamics of the three-dimensional gauge glass
We study the non-equilibrium aging behavior of the gauge glass model in three
dimensions at the critical temperature. We perform Monte Carlo simulations with
a Metropolis update, and correlation and response functions are calculated for
different waiting times. We obtain a multiplicative aging scaling of the
correlation and response functions, calculating the aging exponent and the
nonequilibrium autocorrelation decay exponent . We also analyze
the fluctuation-dissipation relationship at the critical temperature, obtaining
the critical fluctuation-dissipation ratio . By comparing our results
with the aging scaling reported previously for a model of interacting flux
lines in the vortex glass regime, we found that the exponents for both models
are very different.Comment: 7 pages, 4 figures. Manuscript accpeted for publication in PR
Comment on ``Periodic wave functions and number of extended states in random dimer systems'
There are no periodic wave-functions in the RDM but close to the critical
energies there exist periodic envelopes. These envelopes are given by the
non-disordered properties of the system.Comment: RevTex file, 1 page, Comment X. Huang, X. Wu and C. Gong, Phys. Rev.
B 55, 11018 (1997
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