912 research outputs found
Oscillating elastic defects: competition and frustration
We consider a dynamical generalization of the Eshelby problem: the strain
profile due to an inclusion or "defect" in an isotropic elastic medium. We show
that the higher the oscillation frequency of the defect, the more localized is
the strain field around the defect. We then demonstrate that the qualitative
nature of the interaction between two defects is strongly dependent on
separation, frequency and direction, changing from "ferromagnetic" to
"antiferromagnetic" like behavior. We generalize to a finite density of defects
and show that the interactions in assemblies of defects can be mapped to XY
spin-like models, and describe implications for frustration and
frequency-driven pattern transitions.Comment: 4 pages, 5 figure
Density Matrix Renormalization Group study on incommensurate quantum Frenkel-Kontorova model
By using the density matrix renormalization group (DMRG) technique, the
incommensurate quantum Frenkel-Kontorova model is investigated numerically. It
is found that when the quantum fluctuation is strong enough, the
\emph{g}-function featured by a saw-tooth map in the depinned state will show a
different kind of behavior, similar to a standard map, but with reduced
magnitude. The related position correlations are studied in details, which
leads to a potentially interesting application to the recently well-explored
phase transitions in cold atoms loaded in optical lattices.Comment: 11 figures, submitted to Phys. Rev.
Predicting dislocation climb: Classical modeling versus atomistic simulations
The classical modeling of dislocation climb based on a continuous description
of vacancy diffusion is compared to recent atomistic simulations of dislocation
climb in body-centered cubic iron under vacancy supersaturation [Phys. Rev.
Lett. 105 095501 (2010)]. A quantitative agreement is obtained, showing the
ability of the classical approach to describe dislocation climb. The analytical
model is then used to extrapolate dislocation climb velocities to lower
dislocation densities, in the range corresponding to experiments. This allows
testing of the validity of the pure climb creep model proposed by Kabir et al.
[Phys. Rev. Lett. 105 095501 (2010)]
The quantum smectic as a dislocation Higgs phase
The theory describing quantum-smectics in 2+1 dimensions, based on
topological quantum melting is presented. This is governed by a dislocation
condensate characterized by an ordering of Burger's vector and this `dual shear
superconductor' manifests itself in the form of a novel spectrum of phonon-like
modes.Comment: 5 pages, 3 figures; minor changes in the tex
Numerical study of domain coarsening in anisotropic stripe patterns
We study the coarsening of two-dimensional smectic polycrystals characterized
by grains of oblique stripes with only two possible orientations. For this
purpose, an anisotropic Swift-Hohenberg equation is solved. For quenches close
enough to the onset of stripe formation, the average domain size increases with
time as . Further from onset, anisotropic pinning forces similar to
Peierls stresses in solid crystals slow down defects, and growth becomes
anisotropic. In a wide range of quench depths, dislocation arrays remain mobile
and dislocation density roughly decays as , while chevron boundaries
are totally pinned. We discuss some agreements and disagreements found with
recent experimental results on the coarsening of anisotropic electroconvection
patterns.Comment: 8 pages, 11 figures. Phys. Rev E, to appea
Generalized stacking fault energetics and dislocation properties: compact vs. spread unit dislocation structures in TiAl and CuAu
We present a general scheme for analyzing the structure and mobility of
dislocations based on solutions of the Peierls-Nabarro model with a two
component displacement field and restoring forces determined from the ab-initio
generalized stacking fault energetics (ie., the so-called -surface).
The approach is used to investigate dislocations in L1 TiAl and CuAu;
predicted differences in the unit dislocation properties are explicitly related
with features of the -surface geometry. A unified description of
compact, spread and split dislocation cores is provided with an important
characteristic "dissociation path" revealed by this highly tractable scheme.Comment: 7 two columns pages, 2 eps figures. Phys. Rev. B. accepted November
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Shear-melting of a hexagonal columnar crystal by proliferation of dislocations
A hexagonal columnar crystal undergoes a shear-melting transition above a
critical shear rate or stress. We combine the analysis of the shear-thinning
regime below the melting with that of synchrotron X-ray scattering data under
shear and propose the melting to be due to a proliferation of dislocations,
whose density is determined by both techniques to vary as a power law of the
shear rate with a 2/3 exponent, as expected for a creep model of crystalline
solids. Moreover, our data suggest the existence under shear of a line hexatic
phase, between the columnar crystal and the liquid phase
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