2,313 research outputs found
Symmetrical Temperature-Chaos Effect with Positive and Negative Temperature Shifts in a Spin Glass
The aging in a Heisenberg-like spin glass Ag(11 at% Mn) is investigated by
measurements of the zero field cooled magnetic relaxation at a constant
temperature after small temperature shifts . A
crossover from fully accumulative to non-accumulative aging is observed, and by
converting time scales to length scales using the logarithmic growth law of the
droplet model, we find a quantitative evidence that positive and negative
temperature shifts cause an equivalent restart of aging (rejuvenation) in terms
of dynamical length scales. This result supports the existence of a unique
overlap length between a pair of equilibrium states in the spin glass system.Comment: 4 page
Vortex jamming in superconductors and granular rheology
We demonstrate that a highly frustrated anisotropic Josephson junction
array(JJA) on a square lattice exhibits a zero-temperature jamming transition,
which shares much in common with those in granular systems. Anisotropy of the
Josephson couplings along the horizontal and vertical directions plays roles
similar to normal load or density in granular systems. We studied numerically
static and dynamic response of the system against shear, i. e. injection of
external electric current at zero temperature. Current-voltage curves at
various strength of the anisotropy exhibit universal scaling features around
the jamming point much as do the flow curves in granular rheology, shear-stress
vs shear-rate. It turns out that at zero temperature the jamming transition
occurs right at the isotropic coupling and anisotropic JJA behaves as an exotic
fragile vortex matter : it behaves as superconductor (vortex glass) into one
direction while normal conductor (vortex liquid) into the other direction even
at zero temperature. Furthermore we find a variant of the theoretical model for
the anisotropic JJA quantitatively reproduces universal master flow-curves of
the granular systems. Our results suggest an unexpected common paradigm
stretching over seemingly unrelated fields - the rheology of soft materials and
superconductivity.Comment: 10 pages, 5 figures. To appear in New Journal of Physic
Interference Commensurate Oscillations in Q1D Conductors
We suggest an analytical theory to describe angular magnetic oscillations
recently discovered in quasi-one-dimensional conductor (TMTSF)2PF6 [see Phys.
Rev. B, 57, 7423 (1998)] and define the positions of the oscillation minima.
The origin of these oscillations is related to interference effects resulting
from an interplay of quasi-periodic and periodic ("commensurate") electron
trajectories in an inclined magnetic field. We reproduce via calculations
existing experimental data and predict some novel effects.Comment: 10 pages, 2 figure
Memory in aged granular media
Stimulated by recent experimental results, we simulate
``temperature''-cycling experiments in a model for the compaction of granular
media. We report on the existence of two types of memory effects: short-term
dependence on the history of the sample, and long-term memory for highly
compact (aged) systems. A natural interpretation of these results is provided
by the analysis of the density heterogeneities.Comment: 5 eps figures, uses euromacr.tex and europhys.sty (included
Time and length scales in spin glasses
We discuss the slow, nonequilibrium, dynamics of spin glasses in their glassy
phase. We briefly review the present theoretical understanding of the
spectacular phenomena observed in experiments and describe new numerical
results obtained in the first large-scale simulation of the nonequilibrium
dynamics of the three dimensional Heisenberg spin glass.Comment: Paper presented at "Highly Frustrated Magnetism 2003", Grenoble,
August 200
Black Hole Cross Section at the Large Hadron Collider
Black hole production at the Large Hadron Collider (LHC) was first discussed
in 1999. Since then, much work has been performed in predicting the black hole
cross section. In light of the start up of the LHC, it is now timely to review
the state of these calculations. We review the uncertainties in estimating the
black hole cross section in higher dimensions. One would like to make this
estimate as precise as possible since the predicted values, or lower limits,
obtain for the fundamental Planck scale and number of extra dimensions from
experiments will depend directly on the accuracy of the cross section. Based on
the current knowledge of the cross section, we give a range of lower limits on
the fundamental Planck scale that could be obtained at LHC energies.Comment: 28 pages, 9 figures, LaTeX; added references, corrected typos,
expanded discussio
Dynamics of ghost domains in spin-glasses
We revisit the problem of how spin-glasses ``heal'' after being exposed to
tortuous perturbations by the temperature/bond chaos effects in
temperature/bond cycling protocols. Revised scaling arguments suggest the
amplitude of the order parameter within ghost domains recovers very slowly as
compared with the rate it is reduced by the strong perturbations. The parallel
evolution of the order parameter and the size of the ghost domains can be
examined in simulations and experiments by measurements of a memory
auto-correlation function which exhibits a ``memory peak'' at the time scale of
the age imprinted in the ghost domains. These expectations are confirmed by
Monte Calro simulations of an Edwards-Anderson Ising spin-glass model.Comment: 17 pages, 3 figure
Absorption spectrum in the wings of the potassium second resonance doublet broadened by helium
We have measured the reduced absorption coefficients occurring in the wings
of the potassium 4S-5P doublet lines at 404.414 nm and at 404.720 nm broadened
by helium gas at pressures of several hundred Torr. At the experimental
temperature of 900 K, we have detected a shoulder-like broadening feature on
the blue wing of the doublet which is relatively flat between 401.8 nm and
402.8 nm and which drops off rapidly for shorter wavelengths, corresponding to
absorption from the X doublet Sigma+ state to the C doublet Sigma+ state of the
K-He quasimolecule. The accurate measurements of the line profiles in the
present work will sharply constrain future calculations of potential energy
surfaces and transition dipole moments correlating to the asymptotes He-K(5p),
He-K(5s), and He-K(3d).Comment: 2 figure
Analysis on Aging in the Generalized Random Energy Model
A new dynamics more natural than that proposed by Bouchaud and Dean is
introduced to the Generalized Random Energy Model, and the master equation for
the dynamics is solved exactly to calculate the time correlation function.
Although our results are very similar to those obtained by Bouchaud and Dean
qualitatively, the exponents for power law relaxation are different. The
Zero-Field-Cooled magnetization is also calculated with a relation between the
correlation function and the response function which holds even if the
relaxation is non-equilibrium. The validity of these analytic results are
confirmed by numerical simulations.Comment: 12 pages, 5 figures, submitted to J. Phys. Sci. Jp
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