4,924 research outputs found
Eulerian Walkers as a model of Self-Organised Criticality
We propose a new model of self-organized criticality. A particle is dropped
at random on a lattice and moves along directions specified by arrows at each
site. As it moves, it changes the direction of the arrows according to fixed
rules. On closed graphs these walks generate Euler circuits. On open graphs,
the particle eventually leaves the system, and a new particle is then added.
The operators corresponding to particle addition generate an abelian group,
same as the group for the Abelian Sandpile model on the graph. We determine the
critical steady state and some critical exponents exactly, using this
equivalence.Comment: 4 pages, RevTex, 4 figure
Quasiadiabatic dynamics of ultracold bosonic atoms in a one-dimensional optical superlattice
We study the quasiadiabatic dynamics of a one-dimensional system of ultracold
bosonic atoms loaded in an optical superlattice. Focusing on a slow linear
variation in time of the superlattice potential, the system is driven from a
conventional Mott insulator phase to a superlattice-induced Mott insulator,
crossing in between a gapless critical superfluid region. Due to the presence
of a gapless region, a number of defects depending on the velocity of the
quench appear. Our findings suggest a power-law dependence similar to the
Kibble-Zurek mechanism for intermediate values of the quench rate. For the
temporal ranges of the quench dynamics that we considered, the scaling of
defects depends nontrivially on the width of the superfluid region.Comment: 6 Pages, 4 Figure
The Oslo model, hyperuniformity, and the quenched Edwards-Wilkinson model
We present simulations of the 1-dimensional Oslo rice pile model in which the
critical height at each site is randomly reset after each toppling. We use the
fact that the stationary state of this sandpile model is hyperuniform to reach
system of sizes . Most previous simulations were seriously flawed by
important finite size corrections. We find that all critical exponents have
values consistent with simple rationals: for the correlation length
exponent, for the fractal dimension of avalanche clusters, and for the dynamical exponent. In addition we relate the hyperuniformity
exponent to the correlation length exponent . Finally we discuss the
relationship with the quenched Edwards-Wilkinson (qEW) model, where we find in
particular that the local roughness exponent is .Comment: 20 pages, 26 figure
Fast trimers in one-dimensional extended Fermi-Hubbard model
We consider a one-dimensional two component extended Fermi-Hubbard model with
nearest neighbor interactions and mass imbalance between the two species. We
study the stability of trimers, various observables for detecting them, and
expansion dynamics. We generalize the definition of the trimer gap to include
the formation of different types of clusters originating from nearest neighbor
interactions. Expansion dynamics reveal rapidly propagating trimers, with
speeds exceeding doublon propagation in strongly interacting regime. We present
a simple model for understanding this unique feature of the movement of the
trimers, and we discuss the potential for experimental realization.Comment: 10 pages, 10 figure
Zero-temperature Hysteresis in Random-field Ising Model on a Bethe Lattice
We consider the single-spin-flip dynamics of the random-field Ising model on
a Bethe lattice at zero temperature in the presence of a uniform external
field. We determine the average magnetization as the external field is varied
from minus infinity to plus infinity by setting up the self-consistent field
equations, which we show are exact in this case. We find that for a
3-coordinated Bethe lattice, there is no jump discontinuity in magnetization
for arbitrarily small gaussian disorder, but the discontinuity is present for
larger coordination numbers. We have checked our results by Monte Carlo
simulations employing a technique for simulating classical interacting systems
on the Bethe lattice which avoids surface effects altogether.Comment: latex file with 5 eps figures. This version is substantially revised
with new material. Submitted to J. Phys.
Effect of phonon-phonon interactions on localization
We study the heat current J in a classical one-dimensional disordered chain
with on-site pinning and with ends connected to stochastic thermal reservoirs
at different temperatures. In the absence of anharmonicity all modes are
localized and there is a gap in the spectrum. Consequently J decays
exponentially with system size N. Using simulations we find that even a small
amount of anharmonicity leads to a J~1/N dependence, implying diffusive
transport of energy.Comment: 4 pages, 2 figures, Published versio
Magnetic properties of EuPtSi single crystals
Single crystals of EuPtSi, which crystallize in the BaNiSn-type
crystal structure, have been grown by high temperature solution growth method
using molten Sn as the solvent. EuPtSi which lacks the inversion symmetry
and has only one Eu site in the unit cell is found to be an antiferromagnet
with two successive magnetic transitions at = 17 K and = 16 K, as inferred from magnetic susceptibility, heat capacity and
Eu M\"ossbauer measurements. The isothermal magnetization data for [001] reveal a metamagnetic transition at a critical field = 1 T. The magnetization saturates to a moment value of 6.43 /Eu above 5.9 T (9.2 T) for [001] ([100]), indicating that
these fields are spin-flip fields for the divalent Eu moments along the two
axes. The origin of this anisotropic behaviour is discussed. A magnetic (H, T)
phase diagram has been constructed from the temperature dependence of
isothermal magnetization data. The reduced jump in the heat capacity at indicates a transition to an incommensurate, amplitude modulated
antiferromagnetic structure. The shape of the hyperfine field split M\"ossbauer
spectrum at provides additional support for the proposed nature of
this magnetic transition.Comment: 6 pages, 6 figures. Submitted to Phys. Rev.
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