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 $\alpha=-0.011$, $\beta= 0.351$, $\gamma= 1.309$ and $\delta= 4.73$. 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 $F$ 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