34 research outputs found
Single-file diffusion and kinetics of template assisted assembly of colloids
We report computer simulation studies of the kinetics of ordering of a two
dimensional system of particles on a template with a one dimensional periodic
pattern. In equilibrium one obtains a re-entrant liquid-solid-liquid phase
transition as the strength of the substrate potential is varied. We show that
domains of crystalline order grow as , with with a
possible cross-over to at late times. We argue that the
law originates from {\em single-file} motion and annihilation of defect pairs
of opposite topological charge along channels created by the template.Comment: 4 pages pdflatex 4 pdf figure
Spatial stress correlations in strong colloidal gel
In this work, we systematically investigate for the first time the nature of
stress correlations in soft colloidal gel materials which support tensile and
compressive forces as well as finite rolling torque, as a function of system
pressure. Similar to previous studies on frictional granular matter with only
compressive forces and without any rolling torque, the full stress
autocorrelation matrix is dictated by the pressure and torque autocorrelations
due to mechanical balance and material isotropy constraints. Surprisingly, it
is observed that the gel materials do not behave as a normal elastic solid
close to the gel point as assumed loosely in the literature because the real
space pressure fluctuations decay slower than the normal. We also demonstrate
that at low pressure the fractal like structural correlation determines the
pressure fluctuations and this is manifested in the real space in terms of
inhomogeneous and anisotropic force networks formed due to large voids. Far
away from the gel point, as the voids collapse under compression, the force
chain network becomes homogeneous and isotropic and the pressure fluctuations
become normal leading to normal elastic decay at long range, behaving similar
to frictionless granular matter and glass. We also observe that the torque
autocorrelation is not hyperuniform in the presence of rolling resistance close
to the gel point. Furthermore, we link the abnormal pressure fluctuations to
the non-hyperuniform behaviour of the system with respect to the local packing
fraction fluctuations, thus relating the deviations from the normal elastic
behaviour across various non-equilibrium systems under a common framework.Comment: 5 pages, 5 figure
Stress Correlations in Frictional Granular Media
This paper investigates whether in frictional granular packings, like in
Hamiltonian amorphous elastic solids, the stress autocorrelation matrix
presents long range anisotropic contributions just as elastic Green's
functions. We find that in a standard model of frictional granular packing this
is not the case. We prove quite generally that mechanical balance and material
isotropy constrain the stress auto-correlation matrix to be fully determined by
two spatially isotropic functions: the pressure and torque auto-correlations.
The pressure and torque fluctuations being respectively normal and hyperuniform
force the stress autocorrelation to decay as the elastic Green's function.
Since we find the torque fluctuations to be hyper-uniform, the culprit is the
pressure whose fluctuations decay slower than normally as a function of the
system's size. Investigating the reason for these abnormal pressure
fluctuations we discover that anomalous correlations build up already during
the compression of the dilute system before jamming. Once jammed these
correlations remain frozen. Whether this is true for frictional matter in
general or is it the consequence of the model properties is a question that
must await experimental scrutiny and possible alternative models.Comment: 9 Figures, 11 pages: Submitted to Physical Review
Modeling Barkhausen Noise in Magnetic Glasses with Dipole-Dipole Interactions
Long-ranged dipole-dipole interactions in magnetic glasses give rise to
magnetic domains having labyrinthine patterns. Barkhausen Noise is then
expected to result from the movement of domain boundaries which is supposed to
be modeled by the motion of elastic membranes with random pinning. We propose
an atomistic model of such magnetic glasses in which we measure the Barkhausen
Noise which indeed results from the movement of domain boundaries. Nevertheless
the statistics of the Barkhausen Noise is found in striking disagreement with
the expectations in the literature. In fact we find exponential statistics
without any power law, stressing the fact that Barkhausen Noise can belong to
very different universality classes. In this glassy system the essence of the
phenomenon is the ability of spin-carrying particles to move and minimize the
energy without any spin flip. A theory is offered in excellent agreement with
the measured data without any free parameter.Comment: 5 Pages, 5 Figures, Submitted to EP
Universal low-frequency vibrational modes in silica glasses
It was recently shown that different simple models of glass formers with
binary interactions define a universality class in terms of the density of
states of their quasi-localized low-frequency modes. Explicitly, once the
hybridization with standard Debye (extended) modes is avoided, a number of such
models exhibit a universal density of state, depending on the mode frequencies
as . It is unknown however how wide is this
universality class, and whether it also pertains to more realistic models of
glass formers. To address this issue we present analysis of the quasi-localized
modes in silica, a network glass which has both binary and ternary
interactions. We conclude that in 3-dimensions silica exhibits the very same
frequency dependence at low frequencies, suggesting that this universal form is
a generic consequence of amorphous glassiness.Comment: 4 pages, 5 figures, Submitted in parallel to "Universality of the
nonphononic vibrational spectrum across different classes of computer
glasses" to arXiv on March 17th, 202
Magneto-mechanical Coupling in Thermal Amorphous Solids
Standard approaches to magneto-mechanical interactions in thermal magnetic
crystalline solids involve Landau functionals in which the lattice anisotropy
and the resulting magnetization easy axes are taken explicitly into account. In
glassy systems one needs to develop a theory in which the amorphous structure
precludes the existence of an easy axis, and in which the constituent particles
are free to respond to their local amorphous surroundings and the resulting
forces. We present a theory of all the mixed responses of an amorphous solids
to mechanical strains and magnetic fields. Atomistic models are proposed in
which we test the predictions of magnetostriction for both bulk and nano-film
amorphous samples. The application to nano-films with emergent self-affine free
interfaces requires a careful definition of the film 'width' and its change due
to the magnetostriction effect.Comment: 11 figures, 11 pages, regular articl