378 research outputs found
Magnetic relaxation in hard type-II superconductors
Magnetic relaxation in a type-II superconductor is simulated for a range of
temperatures (T) in a simple model of 2D Josephson junction array (JJA) with
finite screening. The high-T phase, that is characterised by a single time
scale \tau_{\alpha}, crosses over to an intermediate phase at a lower
temperature T_{cr} wherein a second time scale \tau_{\beta}<<\tau_{\alpha}
emerges. The relaxation in the time window set by \tau_{\beta} follows power
law which is attributed to self-organization of the magnetic flux during
relaxation. Consequently, for T<T_{cr}, a transition from super-critical
(current density J>J_{c}) to sub-critical (J<J_{c}) state separated by an
intermediate state with frozen dynamics is observed. Both \tau_{\alpha} and
\tau_{\beta} diverges at T_{sc}<T_{cr}, marking the transition into a state
with true persistent current.Comment: 7 Pages (in Europhys format, .sty included), 5 Figures. To appear in
Europhysics Letter
Glass transition in models with controlled frustration
A class of models with self-generated disorder and controlled frustration is
studied. Between the trivial case, where frustration is not present at all, and
the limit case, where frustration is present over every length scale, a region
with local frustration is found where glassy dynamics appears. We suggest that
in this region, the mean field model might undergo a p-spin like transition,
and increasing the range of frustration, a crossover from a 1-step replica
symmetry breaking to a continuous one might be observed.Comment: 4 pages, 6 figure
On the rigidity of a hard sphere glass near random close packing
We study theoretically and numerically the microscopic cause of the
mechanical stability of hard sphere glasses near their maximum packing. We show
that, after coarse-graining over time, the hard sphere interaction can be
described by an effective potential which is exactly logarithmic at the random
close packing . This allows to define normal modes, and to apply recent
results valid for elastic networks: mechanical stability is a non-local
property of the packing geometry, and is characterized by some length scale
which diverges at [1, 2]. We compute the scaling of the bulk and
shear moduli near , and speculate on the possible implications of these
results for the glass transition.Comment: 7 pages, 4 figures. Figure 4 had a wrong unit in abscissa, which was
correcte
Jamming transition in granular media: A mean field approximation and numerical simulations
In order to study analytically the nature of the jamming transition in
granular material, we have considered a cavity method mean field theory, in the
framework of a statistical mechanics approach, based on Edwards' original idea.
For simplicity we have applied the theory to a lattice model and a transition
with exactly the same nature of the glass transition in mean field models for
usual glass formers is found. The model is also simulated in three dimensions
under tap dynamics and a jamming transition with glassy features is observed.
In particular two step decays appear in the relaxation functions and dynamic
heterogeneities resembling ones usually observed in glassy systems. These
results confirm early speculations about the connection between the jamming
transition in granular media and the glass transition in usual glass formers,
giving moreover a precise interpretation of its nature.Comment: 11 pages, 12 figure
Glass transition in the quenched and annealed version of the frustrated lattice gas model
In this paper we study the 3d frustrated lattice gas model in the annealed
version, where the disorder is allowed to evolve in time with a suitable
kinetic constraint. Although the model does not exhibit any thermodynamic
transition it shows a diverging peak at some characteristic time in the
dynamical non-linear susceptibility, similar to the results on the p-spin model
in mean field and Lennard-Jones mixture recently found by Donati et al.
[cond-mat/9905433]. Comparing these results to those obtained in the model with
quenched interactions, we conclude that the critical behavior of the dynamical
susceptibility is reminiscent of the thermodynamic transition present in the
quenched model, and signaled by the divergence of the static non-linear
susceptibility, suggesting therefore a similar mechanism also in supercooled
glass-forming liquids.Comment: 8 pages, 14 figure
Thermodynamic Comparison and the Ideal Glass Transition of A Monatomic Systems Modeled as an Antiferromagnetic Ising Model on Husimi and Cubic Recursive Lattices of the Same Coordination Number
Two kinds of recursive lattices with the same coordination number but
different unit cells (2-D square and 3-D cube) are constructed and the
antiferromagnetic Ising model is solved exactly on them to study the stable and
metastable states. The Ising model with multi-particle interactions is designed
to represent a monatomic system or an alloy. Two solutions of the model exhibit
the crystallization of liquid, and the ideal glass transition of supercooled
liquid respectively. Based on the solutions, the thermodynamics on both
lattices was examined. In particular, the free energy, energy, and entropy of
the ideal glass, supercooled liquid, crystal, and liquid state of the model on
each lattice were calculated and compared with each other. Interactions between
particles farther away than the nearest neighbor distance are taken into
consideration. The two lattices show comparable properties on the transition
temperatures and the thermodynamic behaviors, which proves that both of them
are practical to describe the regular 3-D case, while the different effects of
the unit types are still obvious.Comment: 27 pages, 13 figure
Phase diagram of glassy systems in an external field
We study the mean-field phase diagram of glassy systems in a field pointing
in the direction of a metastable state. We find competition among a
``magnetized'' and a ``disordered'' phase, that are separated by a coexistence
line as in ordinary first order phase transitions. The coexistence line
terminates in a critical point, which in principle can be observed in numerical
simulations of glassy models.Comment: 4 pages, 5 figure
DYNAMICAL SOLUTION OF A MODEL WITHOUT ENERGY BARRIERS
In this note we study the dynamics of a model recently introduced by one of
us, that displays glassy phenomena in absence of energy barriers. Using an
adiabatic hypothesis we derive an equation for the evolution of the energy as a
function of time that describes extremely well the glassy behaviour observed in
Monte Carlo simulations.Comment: 11 pages, LaTeX, 3 uuencoded figure
Glasslike Arrest in Spinodal Decomposition as a Route to Colloidal Gelation
Colloid-polymer mixtures can undergo spinodal decomposition into colloid-rich
and colloid-poor regions. Gelation results when interconnected colloid-rich
regions solidify. We show that this occurs when these regions undergo a glass
transition, leading to dynamic arrest of the spinodal decomposition. The
characteristic length scale of the gel decreases with increasing quench depth,
and the nonergodicity parameter exhibits a pronounced dependence on scattering
vector. Mode coupling theory gives a good description of the dynamics, provided
we use the full static structure as input.Comment: 14 pages, 4 figures; replaced with published versio
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