3,300 research outputs found
Fluctuating Topological Defects in 2D Liquids: Heterogeneous Motion and Noise
We measure the defect density as a function of time at different temperatures
in simulations of a two dimensional system of interacting particles. Just above
the solid to liquid transition temperature, the power spectrum of the defect
fluctuations shows a 1/f signature, which crosses over to a white noise
signature at higher temperatures. When 1/f noise is present, the 5-7 defects
predominately form string like structures, and the particle trajectories show a
1D correlated motion that follows the defect strings. At higher temperatures
this heterogeneous motion is lost. We demonstrate this heterogeneity both in
systems interacting with a short ranged screened Coulomb interaction, as well
as in systems with a long range logarithmic interaction between the particles.Comment: 4 pages, 5 postscript figure
Kinetic Heterogeneities at Dynamical Crossovers
We perform molecular dynamics simulations of a model glass-forming liquid to
measure the size of kinetic heterogeneities, using a dynamic susceptibility
that quantifies the number of particles whose dynamics
are correlated on the length scale and time scale . By measuring
as a function of both and , we locate local maxima
at distances and times . Near the dynamical
glass transition, we find two types of maxima, both correlated with crossovers
in the dynamical behavior: a smaller maximum corresponding to the crossover
from ballistic to sub-diffusive motion, and a larger maximum corresponding to
the crossover from sub-diffusive to diffusive motion. Our results indicate that
kinetic heterogeneities are not necessarily signatures of an impending glass or
jamming transition.Comment: 6 pages, 4 figure
Mean-field glass transition in a model liquid
We investigate the liquid-glass phase transition in a system of point-like
particles interacting via a finite-range attractive potential in D-dimensional
space. The phase transition is driven by an `entropy crisis' where the
available phase space volume collapses dramatically at the transition. We
describe the general strategy underlying the first-principles replica
calculation for this type of transition; its application to our model system
then allows for an analytic description of the liquid-glass phase transition
within a mean-field approximation, provided the parameters are chosen suitably.
We find a transition exhibiting all the features associated with an `entropy
crisis', including the characteristic finite jump of the order parameter at the
transition while the free energy and its first derivative remain continuous.Comment: 12 pages, 6 figure
Following microscopic motion in a two dimensional glass-forming binary fluid
The dynamics of a binary mixture of large and small discs are studied at
temperatures approaching the glass transition using an analysis based on the
topology of the Voronoi polygon surrounding each atom. At higher temperatures
we find that dynamics is dominated by fluid-like motion that involves particles
entering and exiting the nearest-neighbour shells of nearby particles. As the
temperature is lowered, the rate of topological moves decreases and motion
becomes localised to regions of mixed pentagons and heptagons. In addition we
find that in the low temperature state particles may translate significant
distances without undergoing changes in their nearest neig hbour shell. These
results have implications for dynamical heterogeneities in glass forming
liquids.Comment: 12 pages, 7 figure
Localization Properties of Two Interacting Electrons in a Disordered Quasi One-Dimensional Potential
We study the transport properties of two electrons in a quasi one-dimensional
disordered wire. The electrons are subject to both, a disorder potential and a
short range two-body interaction. Using the approach developed by Iida et al. [
Ann. Phys. (N.Y.) 200 (1990) 219 ], the supersymmetry technique, and a suitable
truncation of Hilbert space, we work out the two-point correlation function in
the framework of a non-linear sigma model. We study the loop corrections to
arbitrary order. We obtain a remarkably simple and physically transparent
expression for the change of the localization length caused by the two-body
interaction.Comment: 10 page
Interacting potential between spinons in the compact QED3 description of the Heisenberg model
We implement a Chern-Simons (CS) contribution into the compact QED3
description of the antiferromagnetic Heisenberg model in two dimensions at zero
temperature. The CS term allows for the conservation of the SU(2) symmetry of
the quantum spin system and fixes the flux through a plaquette to be a multiple
of pi as was shown by Marston. We work out the string tension of the confining
potential which acts between the spinons and show that the CS term induces a
screening effect on the magnetic field only. The confining potential between
spinons is not affected by the CS flux. The strict site-occupation by a single
spin 1/2 is enforced by the introduction of an imaginary chemical potential
constraint.Comment: 8 page
Reply to ``Comment on `Hole-burning experiments within glassy models with infinite range interactions' ''
This is a reply to the comments by Richter and Chamberlin, and Diezemann and
Bohmer to our paper (Phys. Rev. Lett. 85, 3448 (2000)). As further evidence for
the claims in this Letter, we here reproduce the nonlinear spectral
hole-burning experimental protocol in an equilibrated fully connected
spin-glass model and we exhibit frequency selectivity, together with a shift in
the base of the spectral hole.Comment: 1 page, two figures, to appear in Phys. Rev. Let
Dynamical and quasistatic structural relaxation paths in Pd_(40)Ni_(40)P_(20) glass
By sequential heat treatment of a Pd_(40)Ni_(40)P_(20) metallic glass at temperatures and durations for which
α-relaxation is not possible, dynamic, and quasistatic relaxation paths below the glass transition are
identified via ex situ ultrasonic measurements following each heat treatment. The dynamic
relaxation paths are associated with hopping between nonequilibrium potential energy states of the
glass, while the quasistatic relaxation path is associated with reversible β-relaxation events toward
quasiequilibrium states. These quasiequilibrium states are identified with secondary potential energy
minima that exist within the inherent energy minimum of the glass, thereby supporting the concept
of the sub-basin/metabasin organization of the potential-energy landscape
Dynamic facilitation explains democratic particle motion of metabasin transitions
Transitions between metabasins in supercooled liquids seem to occur through
rapid "democratic" collective particle rearrangements. Here we show that this
apparent homogeneous particle motion is a direct consequence of dynamic
facilitation. We do so by studying metabasin transitions in facilitated spin
models and constrained lattice gases. We find that metabasin transitions occur
through a sequence of locally facilitated events taking place over a relatively
short time frame. When observed on small enough spatial windows these events
appear sudden and homogeneous. Our results indicate that metabasin transitions
are essentially "non-democratic" in origin and yet another manifestation of
dynamical heterogeneity in glass formers.Comment: 6 pages, 6 figure
Dynamics of glass-forming liquids. XVI. Observation of ultrastable glass transformation via dielectric spectroscopy
The transformation of vapor-deposited ultrastable glasses of indomethacin (IMC) into the supercooled liquid state near Tg is monitored by means of dielectric spectroscopy. Films with thickness between 400 and 800 nm are deposited on differential interdigitated electrode cells and their loss profiles are measured during isothermal annealing using a dual-channel impedance technique for frequencies between 0.03 and 100 Hz. All dielectric loss spectra observed during the transformation process can be explained by a volume fraction of the supercooled liquid that increases linearly with time. From the early stages of the transformation to the liquid that is formed via complete annealing of the ultrastable glass, the average dielectric relaxation time as well as the distribution of relaxation times of the liquid component are identical to those of the conventional liquid obtained by cooling the melt. The dependence of the transformation rate on the film thickness is consistent with a growth front mechanism for the direct conversion from the ultrastable glass to the equilibrium supercooled liquid. We conclude that the IMC liquid recovered from the ultrastable glass is structurally and dynamically identical to the conventional supercooled state
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