11,736 research outputs found
Equilibrium and off-equilibrium simulations of chiral-glass order in three-dimensional Heisenberg spin glasses
Spin-glass and chiral-glass orderings in three-dimensional Heisenberg spin
glasses are studied both by equilibrium and off-equilibrium Monte Carlo
simulations. Fully isotropic model is found to exhibit a finite-temperature
chiral-glass transition without the conventional spin-glass order. Although
chirality is an Ising-like quantity from symmetry, universality class of the
chiral-glass transition appears to be different from that of the standard Ising
spin glass. In the off-equilibrium simulation, while the spin autocorrelation
exhibits only an interrupted aging, the chirality autocorrelation persists to
exhibit a pronounced aging effect reminisecnt of the one observed in the
mean-field model. Effects of random magnetic anisotropy is also studied by the
off-equilibrium simulation, in which asymptotic mixing of the spin and the
chirality is observed.Comment: 15 pages including 8 figures, plain Tex, to appear in Computer
Simulation Studies in Condensed Matter Physics XI, Springer, 199
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
Replica symmetry breaking transition of the weakly anisotropic Heisenberg spin glass in magnetic fields
The spin and the chirality orderings of the three-dimensional Heisenberg spin
glass with the weak random anisotropy are studied under applied magnetic fields
by equilibrium Monte Carlo simulations. A replica symmetry breaking transition
occurs in the chiral sector accompanied by the simultaneous spin-glass order.
The ordering behavior differs significantly from that of the Ising SG, despite
the similarity in the global symmetry. Our observation is consistent with the
spin-chirality decoupling-recoupling scenario of a spin-glass transition.Comment: 4 pages, 4 figure
Vortex glass transition in a frustrated 3D XY model with disorder
The anisotropic frustrated three dimensional (3D) XY model with disorder in
the coupling constants is simulated as a model of a point disordered
superconductor in an applied magnetic field. From a finite size scaling
analysis of the helicity modulus it is concluded that the data is consistent
with a finite temperature transition with isotropic scaling and the correlation
length exponent is found to be \nu=1.50+/-0.12, consistent with 3D gauge glass
universality.Comment: For additional information, see
http://www.tp.umu.se/~olsson/VortexGlass.htm
Ordering of the Heisenberg spin glass in two dimensions
The spin and the chirality orderings of the Heisenberg spin glass in two
dimensions with the nearest-neighbor Gaussian coupling are investigated by
equilibrium Monte Carlo simulations. Particular attention is paid to the
behavior of the spin and the chirality correlation lengths. In order to observe
the true asymptotic behavior, fairly large system size L\gsim 20 (L the linear
dimension of the system) appears to be necessary. It is found that both the
spin and the chirality order only at zero temperature. At high temperatures,
the chiral correlation length stays shorter than spin correlation length,
whereas at lower temperatures below the crossover temperature T_\times, the
chiral correlation length exceeds the spin correlation length. The spin and the
chirality correlation-length exponents are estimated above T_\times to be
\nu_SG=0.9+-0.2 and \nu_CG=2.1+-0.3, respectively. These values are close to
the previous estimates on the basis of the domain-wall-energy calculation.
Discussion is given about the asymptotic critical behavior realized below
T_\times.Comment: to appear in a special issue of J. Phys.
Creep rupture of materials: insights from a fiber bundle model with relaxation
I adapted a model recently introduced in the context of seismic phenomena, to
study creep rupture of materials. It consists of linear elastic fibers that
interact in an equal load sharing scheme, complemented with a local
viscoelastic relaxation mechanism. The model correctly describes the three
stages of the creep process, namely an initial Andrade regime of creep
relaxation, an intermediate regime of rather constant creep rate, and a
tertiary regime of accelerated creep towards final failure of the sample. In
the tertiary regime creep rate follows the experimentally observed one over
time-to-failure dependence. The time of minimum strain rate is systematically
observed to be about 60-65 % of the time to failure, in accordance with
experimental observations. In addition, burst size statistics of breaking
events display a -3/2 power law for events close to the time of failure, and a
steeper decay for the all-time distribution. Statistics of interevent times
shows a tendency of the events to cluster temporarily. This behavior should be
observable in acoustic emission experiments
A Maximum Mass-to-Size Ratio in Scalar-Tensor Theories of Gravity
We derive a modified Buchdahl inequality for scalar-tensor theories of
gravity. In general relativity, Buchdahl has shown that the maximum value of
the mass-to-size ratio, , is 8/9 for static and spherically symmetric
stars under some physically reasonable assumptions. We formally apply
Buchdahl's method to scalar-tensor theories and obtain theory-independent
inequalities. After discussing the mass definition in scalar-tensor theories,
these inequalities are related to a theory-dependent maximum mass-to-size
ratio. We show that its value can exceed not only Buchdahl's limit, 8/9, but
also unity, which we call {\it the black hole limit}, in contrast to general
relativity. Next, we numerically examine the validity of the assumptions made
in deriving the inequalities and the applicability of our analytic results. We
find that the assumptions are mostly satisfied and that the mass-to-size ratio
exceeds both Buchdahl's limit and the black hole limit. However, we also find
that this ratio never exceeds Buchdahl's limit when we impose the further
condition, , on the density, , and pressure, , of the
matter.Comment: 23 pages, 13 figures and 1 tabl
Transversely Polarized Drell-Yan Process and Soft Gluon Resummation in QCD
We calculate the transverse-momentum spectrum of the dilepton in the
transversely polarized Drell-Yan process on the basis of the factorization
theorem in QCD. We take into account universal logarithmically enhanced
corrections in edge region of phase space by resumming multiple soft-gluon
emissions to all orders in the small region.Comment: 84 pages, 5 figures, Revised version published in Prog.Theor.Phy
Electrical polarization of nuclear spins in a breakdown regime of quantum Hall effect
We have developed a method for electrical polarization of nuclear spins in
quantum Hall systems. In a breakdown regime of odd-integer quantum Hall effect
(QHE), excitation of electrons to the upper Landau subband with opposite spin
polarity dynamically polarizes nuclear spins through the hyperfine interaction.
The polarized nuclear spins in turn accelerate the QHE breakdown, leading to
hysteretic voltage-current characteristics of the quantum Hall conductor.Comment: 3 pages, 4 figures, submitted to Appl. Phys. Let
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