1,876 research outputs found
Critical dynamics of diluted relaxational models coupled to a conserved density (diluted model C)
We consider the influence of quenched disorder on the relaxational critical
dynamics of a system characterized by a non-conserved order parameter coupled
to the diffusive dynamics of a conserved scalar density (model C). Disorder
leads to model A critical dynamics in the asymptotics, however it is the
effective critical behavior which is often observed in experiments and in
computer simulations and this is described by the full set of dynamical
equations of diluted model C. Indeed different scenarios of effective critical
behavior are predicted.Comment: 4 pages, 5 figure
Static and dynamic structure factors in three-dimensional randomly diluted Ising models
We consider the three-dimensional randomly diluted Ising model and study the
critical behavior of the static and dynamic spin-spin correlation functions
(static and dynamic structure factors) at the paramagnetic-ferromagnetic
transition in the high-temperature phase. We consider a purely relaxational
dynamics without conservation laws, the so-called model A. We present Monte
Carlo simulations and perturbative field-theoretical calculations. While the
critical behavior of the static structure factor is quite similar to that
occurring in pure Ising systems, the dynamic structure factor shows a
substantially different critical behavior. In particular, the dynamic
correlation function shows a large-time decay rate which is momentum
independent. This effect is not related to the presence of the Griffiths tail,
which is expected to be irrelevant in the critical limit, but rather to the
breaking of translational invariance, which occurs for any sample and which, at
the critical point, is not recovered even after the disorder average.Comment: 43 page
Critical light scattering in liquids
We compare theoretical results for the characteristic frequency of the
Rayleigh peak calculated in one-loop order within the field theoretical method
of the renormalization group theory with experiments and other theoretical
results. Our expressions describe the non-asymptotic crossover in temperature,
density and wave vector. In addition we discuss the frequency dependent shear
viscosity evaluated within the same model and compare our theoretical results
with recent experiments in microgravity.Comment: 17 pages, 12 figure
Model C critical dynamics of random anisotropy magnets
We study the relaxational critical dynamics of the three-dimensional random
anisotropy magnets with the non-conserved n-component order parameter coupled
to a conserved scalar density. In the random anisotropy magnets the structural
disorder is present in a form of local quenched anisotropy axes of random
orientation. When the anisotropy axes are randomly distributed along the edges
of the n-dimensional hypercube, asymptotical dynamical critical properties
coincide with those of the random-site Ising model. However structural disorder
gives rise to considerable effects for non-asymptotic critical dynamics. We
investigate this phenomenon by a field-theoretical renormalization group
analysis in the two-loop order. We study critical slowing down and obtain
quantitative estimates for the effective and asymptotic critical exponents of
the order parameter and scalar density. The results predict complex scenarios
for the effective critical exponent approaching an asymptotic regime.Comment: 8 figures, style files include
XY Spin Fluid in an External Magnetic Field
A method of integral equations is developed to study inhomogeneous fluids
with planar spins in an external field. As a result, the calculations for these
systems appear to be no more difficult than those for ordinary homogeneous
liquids. The approach proposed is applied to the ferromagnetic XY spin fluid in
a magnetic field using a soft mean spherical closure and the Born-Green-Yvon
equation. This provides an accurate reproduction of the complicated phase
diagram behavior obtained by cumbersome Gibbs ensemble simulation and multiple
histogram reweighting techniques.Comment: 4 pages, 3 figures, submitted to Phys. Rev. Let
Resonance statistics in a microwave cavity with a thin antenna
We propose a model for scattering in a flat resonator with a thin antenna.
The results are applied to rectangular microwave cavities. We compute the
resonance spacing distribution and show that it agrees well with experimental
data provided the antenna radius is much smaller than wavelengths of the
resonance wavefunctions.Comment: 10 pages LaTeX source file with one ps figure; to appear in
Phys.Lett.
Concentration and mass dependence of transport coefficients and correlation functions in binary mixtures with high mass-asymmetry
Correlation functions and transport coefficients of self-diffusion and shear
viscosity of a binary Lennard-Jones mixture with components differing only in
their particle mass are studied up to high values of the mass ratio ,
including the limiting case , for different mole fractions .
Within a large range of and the product of the diffusion coefficient
of the heavy species and the total shear viscosity of the mixture
is found to remain constant, obeying a generalized Stokes-Einstein
relation. At high liquid density, large mass ratios lead to a pronounced cage
effect that is observable in the mean square displacement, the velocity
autocorrelation function and the van Hove correlation function
Numerical study of resonant spin relaxation in quasi-1D channels
Recent experiments demonstrate that a ballistic version of spin resonance,
mediated by spin-orbit interaction, can be induced in narrow channels of a
high-mobility GaAs two-dimensional electron gas by matching the spin precession
frequency with the frequency of bouncing trajectories in the channel. Contrary
to the typical suppression of Dyakonov-Perel' spin relaxation in confined
geometries, the spin relaxation rate increases by orders of magnitude on
resonance. Here, we present Monte Carlo simulations of this effect to explore
the roles of varying degrees of disorder and strength of spin-orbit
interaction. These simulations help to extract quantitative spin-orbit
parameters from experimental measurements of ballistic spin resonance, and may
guide the development of future spintronic devices
Gauge dependenceof the order parameter anomalous dimension in the Ginzburg-Landau model and the critical fluctuations in superconductors
The critical fluctuations of superconductors are discussed in a fixed
dimension scaling suited to describe the type II regime. The gauge dependence
of the anomalous dimension of the scalar field is stablished exactly from the
Ward-Takahashi identities. Its fixed point value gives the critical
exponent and it is shown that is gauge independent, as expected on
physical grounds. In the scaling considered, is found to be zero at
1-loop order, while . This result is just the 1-loop values
for the XY model obtained in the fixed dimension renormalization group
approach. It is shown that this XY behavior holds at all orders. The result
should be contrasted with the negative values frequently
reported in the literature.Comment: EuroLaTex, 7 pages, 2 figures, reference updated; version to be
published in Europhysics Letter
- …