2,754 research outputs found
Temperature Chaos, Rejuvenation and Memory in Migdal-Kadanoff Spin Glasses
We use simulations within the Migdal-Kadanoff real space renormalization
approach to probe the scales relevant for rejuvenation and memory in spin
glasses. One of the central questions concerns the role of temperature chaos.
First we investigate scaling laws of equilibrium temperature chaos, finding
super-exponential decay of correlations but no chaos for the total free energy.
Then we perform out of equilibrium simulations that follow experimental
protocols. We find that: (1) rejuvenation arises at a length scale smaller than
the ``overlap length'' l(T,T'); (2) memory survives even if equilibration goes
out to length scales much larger than l(T,T').Comment: 4 pages, 4 figures, added references, slightly changed content,
modified Fig.
A generalized Macdonald operator
We present an explicit difference operator diagonalized by the Macdonald
polynomials associated with an (arbitrary) admissible pair of irreducible
reduced crystallographic root systems. By the duality symmetry, this gives rise
to an explicit Pieri formula for the Macdonald polynomials in question. The
simplest examples of our construction recover Macdonald's celebrated difference
operators and associated Pieri formulas pertaining to the minuscule and
quasi-minuscule weights. As further by-products, explicit expansions and
Littlewood-Richardson type formulas are obtained for the Macdonald polynomials
associated with a special class of small weights.Comment: 11 pages. To appear in Int. Math. Res. Not. IMR
Field-Shift Aging Protocol on the 3D Ising Spin-Glass Model: Dynamical Crossover between the Spin-Glass and Paramagnetic States
Spin-glass (SG) states of the 3-dimensional Ising Edwards-Anderson model
under a static magnetic field are examined by means of the standard Monte
Carlo simulation on the field-shift aging protocol at temperature . For each
process with (T; \tw, h), \tw being the waiting time before the field is
switched on, we extract the dynamical crossover time, \tcr(T; \tw, h). We
have found a nice scaling relation between the two characteristic length scales
which are properly determined from \tcr and \tw and then are normalized by
the static field crossover length introduced in the SG droplet theory. This
scaling behavior implies the instability of the SG phase in the equilibrium
limit even under an infinitesimal . In comparison with this numerical result
the field effect on real spin glasses is also discussed.Comment: 4 pages, 5 figures, jpsj2, Changed conten
Real space application of the mean-field description of spin glass dynamics
The out of equilibrium dynamics of finite dimensional spin glasses is
considered from a point of view going beyond the standard `mean-field theory'
versus `droplet picture' debate of the last decades. The main predictions of
both theories concerning the spin glass dynamics are discussed. It is shown, in
particular, that predictions originating from mean-field ideas concerning the
violations of the fluctuation-dissipation theorem apply quantitatively,
provided one properly takes into account the role of the spin glass coherence
length which plays a central role in the droplet picture. Dynamics in a uniform
magnetic field is also briefly discussed.Comment: 4 pages, 4 eps figures. v2: published versio
Giant Rashba splitting of quasi-1D surface states on Bi/InAs(110)-(21)
Electronic states on the Bi/InAs(110)-(21) surface and its
spin-polarized structure are revealed by angle-resolved photoelectron
spectroscopy (ARPES), spin-resolved ARPES, and density-functional-theory
calculation. The surface state showed quasi-one-dimensional (Q1D) dispersion
and a nearly metallic character; the top of the hole-like surface band is just
below the Fermi level. The size of the Rashba parameter ()
reached quite a large value (5.5 eV\AA). The present result would provide
a fertile playground for further studies of the exotic electronic phenomena in
1D or Q1D systems with the spin-split electronic states as well as for advanced
spintronic devices.Comment: 8 pages (double column), 7 figures and 1 tabl
Aging, rejuvenation and memory effects in Ising and Heisenberg spin glasses
We have compared aging phenomena in the Fe_{0.5}Mn_{0.5}TiO_3 Ising spin
glass and in the CdCr_{1.7}In_{0.3}S_4 Heisenberg-like spin glass by means of
low-frequency ac susceptibility measurements. At constant temperature, aging
obeys the same ` scaling' in both samples as in other systems.
Investigating the effect of temperature variations, we find that the Ising
sample exhibits rejuvenation and memory effects which are qualitatively similar
to those found in other spin glasses, indicating that the existence of these
phenomena does not depend on the dimensionality of the spins. However,
systematic temperature cycling experiments on both samples show important
quantitative differences. In the Ising sample, the contribution of aging at low
temperature to aging at a slightly higher temperature is much larger than
expected from thermal slowing down. This is at variance with the behaviour
observed until now in other spin glasses, which show the opposite trend of a
free-energy barrier growth as the temperature is decreased. We discuss these
results in terms of a strongly renormalized microscopic attempt time for
thermal activation, and estimate the corresponding values of the barrier
exponent introduced in the scaling theories.Comment: 8 pages, including 6 figure
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