1,858 research outputs found
Critical behavior of spin and chiral degrees of freedom in three-dimensional disordered XY models studied by the nonequilibrium aging method
The critical behavior of the gauge-glass and the XY spin-glass models in
three dimensions is studied by analyzing their nonequilibrium aging dynamics. A
new numerical method, which relies on the calculation of the two-time
correlation and integrated response functions, is used to determine both the
critical temperature and the nonequilibrium scaling exponents, both for spin
and chiral degrees of freedom. First, the ferromagnetic XY model is studied to
validate this nonequilibirum aging method (NAM), since for this nondisordered
system we can compare with known results obtained with standard equilibrium and
nonequilibrium techniques. When applied to the case of the gauge-glass model,
we show that the NAM allows us to obtain precise and reliable values of its
critical quantities, improving previous estimates. The XY spin-glass model with
both Gaussian and bimodal bond distributions, is analyzed in more detail. The
spin and the chiral two-time correlation and integrated response functions are
calculated in our simulations. The results obtained mainly for Gaussian and, to
a lesser extent, for bimodal interactions, support the existence of a
spin-chiral decoupling scenario, where the chiral order occurs at a finite
temperature while the spin degrees of freedom order at very low or zero
temperature.Comment: 15 pages, 15 figures. Phys. Rev. B 89, 024408 (2014
Unconventional critical activated scaling of two-dimensional quantum spin-glasses
We study the critical behavior of two-dimensional short-range quantum spin
glasses by numerical simulations. Using a parallel tempering algorithm, we
calculate the Binder cumulant for the Ising spin glass in a transverse magnetic
field with two different short-range bond distributions, the bimodal and the
Gaussian ones. Through an exhaustive finite-size scaling analysis, we show that
the universality class does not depend on the exact form of the bond
distribution but, most important, that the quantum critical behavior is
governed by an infinite randomness fixed point.Comment: 6 pages, 6 figure
Nonequilibrium dynamics of the three-dimensional Edwards-Anderson spin-glass model with Gaussian couplings: Strong heterogeneities and the backbone picture
We numerically study the three-dimensional Edwards-Anderson model with
Gaussian couplings, focusing on the heterogeneities arising in its
nonequilibrium dynamics. Results are analyzed in terms of the backbone picture,
which links strong dynamical heterogeneities to spatial heterogeneities
emerging from the correlation of local rigidity of the bond network. Different
two-times quantities as the flipping time distribution and the correlation and
response functions, are evaluated over the full system and over high- and
low-rigidity regions. We find that the nonequilibrium dynamics of the model is
highly correlated to spatial heterogeneities. Also, we observe a similar
physical behavior to that previously found in the Edwards-Anderson model with a
bimodal (discrete) bond distribution. Namely, the backbone behaves as the main
structure that supports the spin-glass phase, within which a sort of
domain-growth process develops, while the complement remains in a paramagnetic
phase, even below the critical temperature
Influence of the Ground-State Topology on the Domain-Wall Energy in the Edwards-Anderson +/- J Spin Glass Model
We study the phase stability of the Edwards-Anderson spin-glass model by
analyzing the domain-wall energy. For the bimodal distribution of bonds, a
topological analysis of the ground state allows us to separate the system into
two regions: the backbone and its environment. We find that the distributions
of domain-wall energies are very different in these two regions for the three
dimensional (3D) case. Although the backbone turns out to have a very high
phase stability, the combined effect of these excitations and correlations
produces the low global stability displayed by the system as a whole. On the
other hand, in two dimensions (2D) we find that the surface of the excitations
avoids the backbone. Our results confirm that a narrow connection exists
between the phase stability of the system and the internal structure of the
ground-state. In addition, for both 3D and 2D we are able to obtain the fractal
dimension of the domain wall by direct means.Comment: 4 pages, 3 figures. Accepted for publication in Rapid Communications
of Phys. Rev.
Backbone structure of the Edwards-Anderson spin-glass model
We study the ground-state spatial heterogeneities of the Edwards-Anderson
spin-glass model with both bimodal and Gaussian bond distributions. We
characterize these heterogeneities by using a general definition of bond
rigidity, which allows us to classify the bonds of the system into two sets,
the backbone and its complement, with very different properties. This
generalizes to continuous distributions of bonds the well known definition of a
backbone for discrete bond distributions. By extensive numerical simulations we
find that the topological structure of the backbone for a given lattice
dimensionality is very similar for both discrete and continuous bond
distributions. We then analyze how these heterogeneities influence the
equilibrium properties at finite temperature and we discuss the possibility
that a suitable backbone picture can be relevant to describe spin-glass
phenomena.Comment: 12 pages, 10 figure
New combinations for two hybrids in Salvia subg. Rosmarinus (Lamiaceae)
New combinations for two hybrids in Salvia subg. Rosmarinus (Lamiaceae
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