43,172 research outputs found
Structural and dynamical features of multiple metastable glassy states in a colloidal system with competing interactions
Systems in which a short-ranged attraction and long-ranged repulsion compete
are intrinsically frustrated, leading their structure and dynamics to be
dominated either by mesoscopic order or by metastable disorder. Here we report
the latter case in a colloidal system with long-ranged electrostatic repulsions
and short-ranged depletion attractions. We find a variety of states exhibiting
slow non-diffusive dynamics: a gel, a glassy state of clusters, and a state
reminiscent of a Wigner glass. Varying the interactions, we find a continuous
crossover between the Wigner and cluster glassy states, and a sharp
discontinuous transition between the Wigner glassy state and gel. This
difference reflects the fact that dynamic arrest is driven by repulsion for the
two glassy states and attraction in the case of the gel
Defects and glassy dynamics in solid He-4: Perspectives and current status
We review the anomalous behavior of solid He-4 at low temperatures with
particular attention to the role of structural defects present in solid. The
discussion centers around the possible role of two level systems and structural
glassy components for inducing the observed anomalies. We propose that the
origin of glassy behavior is due to the dynamics of defects like dislocations
formed in He-4. Within the developed framework of glassy components in a solid,
we give a summary of the results and predictions for the effects that cover the
mechanical, thermodynamic, viscoelastic, and electro-elastic contributions of
the glassy response of solid He-4. Our proposed glass model for solid He-4 has
several implications: (1) The anomalous properties of He-4 can be accounted for
by allowing defects to freeze out at lowest temperatures. The dynamics of solid
He-4 is governed by glasslike (glassy) relaxation processes and the
distribution of relaxation times varies significantly between different
torsional oscillator, shear modulus, and dielectric function experiments. (2)
Any defect freeze-out will be accompanied by thermodynamic signatures
consistent with entropy contributions from defects. It follows that such
entropy contribution is much smaller than the required superfluid fraction, yet
it is sufficient to account for excess entropy at lowest temperatures. (3) We
predict a Cole-Cole type relation between the real and imaginary part of the
response functions for rotational and planar shear that is occurring due to the
dynamics of defects. Similar results apply for other response functions. (4)
Using the framework of glassy dynamics, we predict low-frequency yet to be
measured electro-elastic features in defect rich He-4 crystals. These
predictions allow one to directly test the ideas and very presence of glassy
contributions in He-4.Comment: 33 pages, 13 figure
Slow dynamics in glassy soft matter
Measuring, characterizing and modelling the slow dynamics of glassy soft
matter is a great challenge, with an impact that ranges from industrial
applications to fundamental issues in modern statistical physics, such as the
glass transition and the description of out-of-equilibrium systems. Although
our understanding of these phenomena is still far from complete, recent
simulations and novel theoretical approaches and experimental methods have shed
new light on the dynamics of soft glassy materials. In this paper, we review
the work of the last few years, with an emphasis on experiments in four
distinct and yet related areas: the existence of two different glass states
(attractive and repulsive), the dynamics of systems very far from equilibrium,
the effect of an external perturbation on glassy materials, and dynamical
heterogeneity
Thermodynamic picture of the glassy state gained from exactly solvable models
A picture for thermodynamics of the glassy state was introduced recently by
us (Phys. Rev. Lett. {\bf 79} (1997) 1317; {\bf 80} (1998) 5580). It starts by
assuming that one extra parameter, the effective temperature, is needed to
describe the glassy state. This approach connects responses of macroscopic
observables to a field change with their temporal fluctuations, and with the
fluctuation-dissipation relation, in a generalized, non-equilibrium way.
Similar universal relations do not hold between energy fluctuations and the
specific heat.
In the present paper the underlying arguments are discussed in greater
length. The main part of the paper involves details of the exact dynamical
solution of two simple models introduced recently: uncoupled harmonic
oscillators subject to parallel Monte Carlo dynamics, and independent spherical
spins in a random field with such dynamics. At low temperature the relaxation
time of both models diverges as an Arrhenius law, which causes glassy behavior
in typical situations. In the glassy regime we are able to verify the above
mentioned relations for the thermodynamics of the glassy state.
In the course of the analysis it is argued that stretched exponential
behavior is not a fundamental property of the glassy state, though it may be
useful for fitting in a limited parameter regime.Comment: revised version, 38 pages, 9 figure
Glassy dynamics in granular compaction
Two models are presented to study the influence of slow dynamics on granular
compaction. It is found in both cases that high values of packing fraction are
achieved only by the slow relaxation of cooperative structures. Ongoing work to
study the full implications of these results is discussed.Comment: 12 pages, 9 figures; accepted in J. Phys: Condensed Matter,
proceedings of the Trieste workshop on 'Unifying concepts in glass physics
Glassy dynamics near zero temperature
We numerically study finite-dimensional spin glasses at low and zero
temperature, finding evidences for (i) strong time/space heterogeneities, (ii)
spontaneous time scale separation and (iii) power law distributions of flipping
times. Using zero temperature dynamics we study blocking, clustering and
persistence phenomena
Landau theory of glassy dynamics
An exact solution of a Landau model of an order-disorder transition with
activated critical dynamics is presented. The model describes a funnel-shaped
topography of the order parameter space in which the number of energy lowering
trajectories rapidly diminishes as the ordered ground-state is approached. This
leads to an asymmetry in the effective transition rates which results in a
non-exponential relaxation of the order-parameter fluctuations and a
Vogel-Fulcher-Tammann divergence of the relaxation times, typical of a glass
transition. We argue that the Landau model provides a general framework for
studying glassy dynamics in a variety of systems.Comment: 4 pages, 2 figure
Slow Dynamics in Glasses
We will review some of the theoretical progresses that have been recently
done in the study of slow dynamics of glassy systems: the general techniques
used for studying the dynamics in the mean field approximation and the
emergence of a pure dynamical transition in some of these systems. We show how
the results obtained for a random Hamiltonian may be also applied to a given
Hamiltonian. These two results open the way to a better understanding of the
glassy transition in real systems
- …