73 research outputs found
Numerical studies of the 2 and 3D gauge glass at low temperature
We report results from Monte Carlo simulations of the two- and
three-dimensional gauge glass at low temperature using parallel tempering Monte
Carlo. In two dimensions, we find strong evidence for a zero-temperature
transition. By means of finite-size scaling, we determine the stiffness
exponent theta = -0.39 +/- 0.03. In three dimensions, where a
finite-temperature transition is well established, we find theta = 0.27 +/-
0.01, compatible with recent results from domain-wall renormalization group
studies.Comment: 3 pages, 3 figures. Proceedings of "2002 MMM Conference", Tampa, F
Ordering of the three-dimensional Heisenberg spin glass in magnetic fields
Spin and chirality orderings of the three-dimensional Heisenberg spin glass
are studied under magnetic fields in light of the recently developed
spin-chirality decoupling-recoupling scenario. It is found by Monte Carlo
simulations that the chiral-glass transition and the chiral-glass ordered
state, which are essentially of the same character as their zero-field
counterparts, occur under magnetic fields. Implication to experimental phase
diagram is discussed.Comment: 5 pages, 3 figure
The Lower Critical Dimension of the XY Spin Glass
We investigate the XY spin-glass model in two and three dimensions using the
domain-wall renormalization-group method. The results for systems of linear
sizes up to L=12 (2D) and L=8 (3D) strongly suggest that the lower critical
dimension for spin-glass ordering may be rather than four as
is commonly believed. Our 3D data favor the scenario of a low but finite
spin-glass ordering temperature below the chiral transition but they are also
compatible with the system being at or slightly below its lower critical
dimension.Comment: 4 pages, 3 ps figures. Typos have been corrected, one reference has
been added and the concluding paragraph has been expanded. To appear in Phys.
Rev. Let
Numerical Study of Spin and Chiral Order in a Two-Dimensional XY Spin Glass
The two dimensional XY spin glass is studied numerically by a finite size
scaling method at T=0 in the vortex representation which allows us to compute
the exact (in principle) spin and chiral domain wall energies. We confirm
earlier predictions that there is no glass phase at any finite T. Our results
strongly support the conjecture that both spin and chiral order have the same
correlation length exponent . We obtain preliminary results
in 3d.Comment: 4 pages, 2 figures, revte
Application of a minimum cost flow algorithm to the three-dimensional gauge glass model with screening
We study the three-dimensional gauge glass model in the limit of strong
screening by using a minimum cost flow algorithm, enabling us to obtain EXACT
ground states for systems of linear size L<=48. By calculating the domain-wall
energy, we obtain the stiffness exponent theta = -0.95+/-0.03, indicating the
absence of a finite temperature phase transition, and the thermal exponent
nu=1.05+/-0.03. We discuss the sensitivity of the ground state with respect to
small perturbations of the disorder and determine the overlap length, which is
characterized by the chaos exponent zeta=3.9+/-0.2, implying strong chaos.Comment: 4 pages RevTeX, 2 eps-figures include
Numerical study of the strongly screened vortex glass model in an external field
The vortex glass model for a disordered high-T_c superconductor in an
external magnetic field is studied in the strong screening limit. With exact
ground state (i.e. T=0) calculations we show that 1) the ground state of the
vortex configuration varies drastically with infinitesimal variations of the
strength of the external field, 2) the minimum energy of global excitation
loops of length scale L do not depend on the strength of the external field,
however 3) the excitation loops themself depend sensibly on the field. From 2)
we infer the absence of a true superconducting state at any finite temperature
independent of the external field.Comment: 6 pages RevTeX, 5 eps-figures include
Phase Transitions in the Two-Dimensional XY Model with Random Phases: a Monte Carlo Study
We study the two-dimensional XY model with quenched random phases by Monte
Carlo simulation and finite-size scaling analysis. We determine the phase
diagram of the model and study its critical behavior as a function of disorder
and temperature. If the strength of the randomness is less than a critical
value, , the system has a Kosterlitz-Thouless (KT) phase transition
from the paramagnetic phase to a state with quasi-long-range order. Our data
suggest that the latter exists down to T=0 in contradiction with theories that
predict the appearance of a low-temperature reentrant phase. At the critical
disorder and for there is no
quasi-ordered phase. At zero temperature there is a phase transition between
two different glassy states at . The functional dependence of the
correlation length on suggests that this transition corresponds to the
disorder-driven unbinding of vortex pairs.Comment: LaTex file and 18 figure
Numerical Study of Order in a Gauge Glass Model
The XY model with quenched random phase shifts is studied by a T=0 finite
size defect energy scaling method in 2d and 3d. The defect energy is defined by
a change in the boundary conditions from those compatible with the true ground
state configuration for a given realization of disorder. A numerical technique,
which is exact in principle, is used to evaluate this energy and to estimate
the stiffness exponent . This method gives in
2d and in 3d, which are considerably larger than
previous estimates, strongly suggesting that the lower critical dimension is
less than three. Some arguments in favor of these new estimates are given.Comment: 4 pages, 2 figures, revtex. Submitted to Phys. Rev. Let
Domain growth by isothermal aging in 3d Ising and Heisenberg spin glasses
Non-equilibrium dynamics of three dimensional model spin glasses - the Ising
system FeMnTiO and the Heisenberg like system Ag(11 at%
Mn) - has been investigated by measurements of the isothermal time decay of the
low frequency ac-susceptibility after a quench from the paramagnetic to the
spin glass phase. It is found that the relaxation data measured at different
temperatures can be scaled according to predictions from the droplet scaling
model, provided that critical fluctuations are accounted for in the analyzes.Comment: 5 pages, 3 figure
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