1,864 research outputs found
Random Field Ising Model In and Out of Equilibrium
We present numerical studies of zero-temperature Gaussian random-field Ising
model (zt-GRFIM) in both equilibrium and non-equilibrium. We compare the
no-passing rule, mean-field exponents and universal quantities in 3D (avalanche
critical exponents, fractal dimensions, scaling functions and anisotropy
measures) for the equilibrium and non-equilibrium disorder-induced phase
transitions. We show compelling evidence that the two transitions belong to the
same universality class.Comment: 4 pages, 2 figures. submitted to Phys. Rev. Let
No-passing Rule in the Ground State Evolution of the Random-Field Ising Model
We exactly prove the no-passing rule in the ground state evolution of the
random-field Ising model (RFIM) with monotonically varying external field. In
particular, we show that the application of the no-passing rule can speed up
the calculation of the zero-temperature equilibrium curve dramatically.Comment: 7 pages, 4 figure
Transforming mesoscale granular plasticity through particle shape
When an amorphous material is strained beyond the point of yielding it enters
a state of continual reconfiguration via dissipative, avalanche-like slip
events that relieve built-up local stress. However, how the statistics of such
events depend on local interactions among the constituent units remains
debated. To address this we perform experiments on granular material in which
we use particle shape to vary the interactions systematically. Granular
material, confined under constant pressure boundary conditions, is uniaxially
compressed while stress is measured and internal rearrangements are imaged with
x-rays. We introduce volatility, a quantity from economic theory, as a powerful
new tool to quantify the magnitude of stress fluctuations, finding systematic,
shape-dependent trends. For all 22 investigated shapes the magnitude of
relaxation events is well-fit by a truncated power law distribution , as has been proposed within the context of plasticity
models. The power law exponent for all shapes tested clusters around
1.5, within experimental uncertainty covering the range 1.3 - 1.7. The
shape independence of and its compatibility with mean field models
indicate that the granularity of the system, but not particle shape, modifies
the stress redistribution after a slip event away from that of continuum
elasticity. Meanwhile, the characteristic maximum event size changes by
two orders of magnitude and tracks the shape dependence of volatility. Particle
shape in granular materials is therefore a powerful new factor influencing the
distance at which an amorphous system operates from scale-free criticality.
These experimental results are not captured by current models and suggest a
need to reexamine the mechanisms driving mesoscale plastic deformation in
amorphous systems.Comment: 11 pages, 8 figures. v3 adds a new appendix and figure about event
rates and changes several parts the tex
Noise Predictions for STM in Systems with Local Electron Nematic Order
We propose that thermal noise in local stripe orientation should be readily
detectable via STM on systems in which local stripe orientations are strongly
affected by quenched disorder. Stripes, a unidirectional, nanoscale modulation
of electronic charge, are strongly affected by quenched disorder in
two-dimensional and quasi-two-dimensional systems. While stripe orientations
tend to lock to major lattice directions, dopant disorder locally breaks
rotational symmetry. In a host crystal with otherwise rotational
symmetry, stripe orientations in the presence of quenched disorder map to the
random field Ising model. While the low temperature state of such a system is
generally a stripe glass in two dimensional or strongly layered systems, as the
temperature is raised, stripe orientational fluctuations become more prevalent.
We propose that these thermally excited fluctuations should be readily
detectable in scanning tunneling spectroscopy as {\em telegraph noise} in the
high voltage part of the local curves. We predict the spatial, temporal,
and thermal evolution of such noise, including the circumstances under which
such noise is most likely to be observed. In addition, we propose an in-situ
test, amenable to any local scanning probe, for assessing whether such noise is
due to correlated fluctuations rather than independent switchers.Comment: 8 pages, 8 figure
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