1,721,030 research outputs found
The critical behavior of 3D Ising glass models: universality and scaling corrections
No full textWe perform high-statistics Monte Carlo simulations of three three-dimensional
Ising spin-glass models: the +-J Ising model for two values of the disorder
parameter p, p=1/2 and p=0.7, and the bond-diluted +-J model for
bond-occupation probability p_b = 0.45. A finite-size scaling analysis of the
quartic cumulants at the critical point shows conclusively that these models
belong to the same universality class and allows us to estimate the
scaling-correction exponent omega related to the leading irrelevant operator,
omega=1.0(1). We also determine the critical exponents nu and eta. Taking into
account the scaling corrections, we obtain nu=2.53(8) and eta=-0.384(9)
Anisotropic perturbations in three-dimensional O(N)-symmetric vector models
No full textWe investigate the effects of anisotropic perturbations in three-dimensional O(N)-symmetric vector models. In order to assess their relevance for the critical behavior, we determine the renormalization-group dimensions of the anisotropic perturbations associated with the first few spin values of the representations of the O(N) group, because the lowest spin values give rise to the most important effects. In particular, we determine them up to spin 4 for N = 2, 3, 4, by finite-size analyses of Monte Carlo simulations of lattice O(N) models, achieving a significant improvement of their accuracy. These results are relevant for several physical systems, such as density-wave systems, magnets with cubic symmetry, and multicritical phenomena arising from the competition of different order parameters
The critical behavior of 3D Ising spin glass models: universality and scaling corrections
No full text
Critical behavior of two-dimensional fully frustrated XY systems
No full textWe study the phase diagram of the two-dimensional fully frustrated XY model
(FFXY) and of two related models, a lattice discretization of the
Landau-Ginzburg-Wilson Hamiltonian for the critical modes of the FFXY model,
and a coupled Ising-XY model. We present Monte Carlo simulations on square
lattices , . We show that the low-temperature phase
of these models is controlled by the same line of Gaussian fixed points as in
the standard XY model. We find that, if a model undergoes a unique transition
by varying temperature, then the transition is of first order. In the opposite
case we observe two very close transitions: a transition associated with the
spin degrees of freedom and, as temperature increases, a transition where
chiral modes become critical. If they are continuous, they belong to the
Kosterlitz-Thouless and to the Ising universality class, respectively. Ising
and Kosterlitz-Thouless behavior is observed only after a preasymptotic regime,
which is universal to some extent. In the chiral case, the approach is
nonmonotonic for most observables, and there is a wide region in which
finite-size scaling is controlled by an effective exponent . This explains the result of many previous
studies using smaller lattices
Universal dependence on disorder of two-dimensional randomly diluted and random-bond +/- J Ising models
No full textMagnetic-glassy multicritical behavior of the three-dimensional +- J Ising model
No full textWe consider the three-dimensional model defined on a simple cubic
lattice and study its behavior close to the multicritical Nishimori point where
the paramagnetic-ferromagnetic, the paramagnetic-glassy, and the
ferromagnetic-glassy transition lines meet in the T-p phase diagram (p
characterizes the disorder distribution and gives the fraction of ferromagnetic
bonds). For this purpose we perform Monte Carlo simulations on cubic lattices
of size and a finite-size scaling analysis of the numerical results.
The magnetic-glassy multicritical point is found at , along the
Nishimori line given by . We determine the
renormalization-group dimensions of the operators that control the
renormalization-group flow close to the multicritical point, ,
, and the susceptibility exponent . The
temperature and crossover exponents are and , respectively. We also investigate the model-A dynamics, obtaining
the dynamic critical exponent
Critical exponents and equation of state of three-dimensional spin models
No full textThree-dimensional spin models of the Ising and XY universality classes are
studied by a combination of high-temperature expansions and Monte Carlo
simulations. Critical exponents are determined to very high precision. Scaling
amplitude ratios are computed via the critical equation of state. Our results
are compared with other theoretical computations and with experiments, with
special emphasis on the lambda transition of 4He
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