450 research outputs found
CRITICAL EXPONENTS OF THE 3D ANTIFERROMAGNETIC THREE-STATE POTTS MODEL USING THE COHERENT-ANOMALY METHOD
The antiferromagnetic three-state Potts model on the simple-cubic lattice is
studied using the coherent-anomaly method (CAM). The CAM analysis provides the
estimates for the critical exponents which indicate the XY universality class,
namely , , and .
This observation corroborates the results of the recent Monte Carlo
simulations, and disagrees with the proposal of a new universality class.Comment: 11 pages, latex, 1 postscript figure, changes: an incorrect reference
omitte
Accurate Estimates of 3D Ising Critical Exponents Using the Coherent-Anomaly Method
An analysis of the critical behavior of the three-dimensional Ising model
using the coherent-anomaly method (CAM) is presented. Various sources of errors
in CAM estimates of critical exponents are discussed, and an improved scheme
for the CAM data analysis is tested. Using a set of mean-field type
approximations based on the variational series expansion approach, accuracy
comparable to the most precise conventional methods has been achieved. Our
results for the critical exponents are given by \alpha=\afin, \beta=\bfin,
\gamma=\gfin and \delta=\dfin.Comment: 16 pages, latex, 1 postscript figur
Universal long-wavelength nonlinear optical response of noble gases
We demonstrate numerically that the long-wavelength nonlinear dipole moment
and ionization rate versus electric field strength for different noble
gases can be scaled onto each other, revealing universal functions that
characterize the form of the nonlinear response. We elucidate the physical
origin of the universality by using a metastable state analysis of the
light-atom interaction in combination with a scaling analysis. Our results also
provide a powerful new means of characterizing the nonlinear response in the
mid-infrared and long-wave infrared for optical filamentation studies.Comment: 8 pages, 6 figure
Magnetization Switching in Single-Domain Ferromagnets
A model for single-domain uniaxial ferromagnetic particles with high
anisotropy, the Ising model, is studied. Recent experimental observations have
been made of the probability that the magnetization has not switched. Here an
approach is described in which it is emphasized that a ferromagnetic particle
in an unfavorable field is in fact a metastable system, and the switching is
accomplished through the nucleation and subsequent growth of localized
droplets. Nucleation theory is applied to finite systems to determine the
coercivity as a function of particle size and to calculate the probability of
not switching. Both of these quantities are modified by different boundary
conditions, magnetostatic interactions, and quenched disorder.Comment: 4 pages, LaTeX, 2 figures, documentstyle{elsart} More fits and
Mathematica notebook at http://www.scri.fsu.edu/~novotny/magnetism.html To
appear in J.Mag.Mag.Mater. Conference Proceedings of 7th International
Conference on Magnetism Cairns, Australia, August, 199
ON THE LOW-TEMPERATURE ORDERING OF THE 3D ATIFERROMAGNETIC THREE-STATE POTTS MODEL
The antiferromagnetic three-state Potts model on the simple-cubic lattice is
studied using Monte Carlo simulations. The ordering in a medium temperature
range below the critical point is investigated in detail. Two different regimes
have been observed: The so-called broken sublattice-symmetry phase dominates at
sufficiently low temperatures, while the phase just below the critical point is
characterized by an effectively continuous order parameter and by a fully
restored rotational symmetry. However, the later phase is not the
permutationally sublattice symmetric phase recently predicted by the cluster
variation method.Comment: 20 pages with 9 figures in a single postscript file (compressed and
uuencoded by uufiles -gz -9) plus two big figures in postscript file
Which part of the Brillouin zone contributes most to the high-harmonic radiation?
Utilizing realistic simulations of high-harmonic generation (HHG) in several
materials, we study how different regions of the Brillouin zone contribute to
the nonlinear response. It is often assumed that only the vicinity of the Gamma
point is predominantly responsible for the HHG spectrum, but it is shown here
that such an approximation is inaccurate in general. While examples can be
identified where merely 0.4% of the Brillouin zone produces semi-quantitatively
accurate HHG-spectra, in most situations one must include at least thirty to
fifty percent of the Brillouin-zone volume to obtain accurate above-the-gap
harmonics. For the harmonic peaks below the bandgap energy, the current-density
responses from the entire Brillouin zone must always be integrated. We also
identify the minimal set of electronic bands necessary for the construction of
reduced but still realistic HHG-models. The results should be useful for a
number of HHG applications, including all-optical reconstructions of the
band-structure and light-matter couplings, or considerations involving
semi-classical approaches to solid-state high-harmonic radiation
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