36 research outputs found
Hysteresis behavior in current-driven stationary resonance induced by nonlinearity in the coupled sine-Gordon equation
Recently novel current-driven resonant states characterized by the
-phase kinks were proposed in the coupled sine-Gordon equation. In these
states hysteresis behavior is observed with respect to the application process
of current, and such behavior is due to nonlinearity in the sine term. Varying
strength of the sine term, there exists a critical strength for the hysteresis
behavior and the amplitude of the sine term coincides with the applied current
at the critical strength.Comment: 3 pages, 3 figures, RevTeX
Stationary phase-kink states and dynamical phase transitions controlled by surface impedance in THz wave emission from intrinsic Josephson junctions
As possible states to characterize THz wave emission from intrinsic Josephson
junctions without external fields, the McCumber-like state and -phase-kink
state have been proposed. In the present article it is numerically shown that
both states are stationary according to the bias current and surface
impedance . The McCumber-like state is stable for low and small . For
higher , the -phase-kink state accompanied with symmetry breaking along
the c axis is stable even for Z=1, though strong emission in the vicinity of
cavity resonance points only takes place for larger . Different emission
behaviors for Z=1 and 10 are precisely compared. The dynamical phase diagram
for and the optimal value of for the strongest emission
are also evaluated.Comment: 4 pages, 8 figures, RevTe
New quantum Monte Carlo study of quantum critical phenomena with Trotter-number-dependent finite-size scaling and non-equilibrium relaxation
We propose a new efficient scheme for the quantum Monte Carlo study of
quantum critical phenomena in quantum spin systems. Rieger and Young's
Trotter-number-dependent finite-size scaling in quantum spin systems and Ito
{\it et al.}'s evaluation of the transition point with the non-equilibrium
relaxation in classical spin systems are combined and generalized. That is,
only one Trotter number and one inverse temperature proportional to system
sizes are taken for each system size, and the transition point of the
transformed classical spin model is estimated as the point at which the order
parameter shows power-law decay. The present scheme is confirmed by the
determination of the critical phenomenon of the one-dimensional
asymmetric XY model in the ground state. The estimates of the transition point
and the critical exponents , and are in good agreement
with the exact solutions. The dynamical critical exponent is also estimated as
{\mit \Delta}=2.14(I4(Jpm 0.06, which is consistent with that of the
two-dimensional Ising model.Comment: 15 pages, 17 Postscript figures, LaTeX, J. Phys. A in pres
New Nonequilibrium-to-Equilibrium Dynamical Scaling and Stretched-Exponential Critical Relaxation in Cluster Algorithms
Nonequilibrium relaxation behaviors in the Ising model on a square lattice
based on the Wolff algorithm are totally different from those based on
local-update algorithms. In particular, the critical relaxation is described by
the stretched-exponential decay. We propose a novel scaling procedure to
connect nonequilibrium and equilibrium behaviors continuously, and find that
the stretched-exponential scaling region in the Wolff algorithm is as wide as
the power-law scaling region in local-update algorithms. We also find that
relaxation to the spontaneous magnetization in the ordered phase is
characterized by the exponential decay, not the stretched-exponential decay
based on local-update algorithms.Comment: J. Phys. Soc. Jpn. 83 (2014) in press; 5 pages, 5 figures, jpsj3.cls
Ver.1.
Energy landscape and shear modulus of interlayer Josephson vortex systems
The ground state of interlayer Josephson vortex systems is investigated on
the basis of a simplified Lawrence-Doniach model in which spatial dependence of
the gauge field and the amplitude of superconducting order parameter is not
taken into account. Energy landscape is drawn with respect to the in-plane
field, the period of insulating layers including Josephson vortices, and the
shift from the aligned vortex lattice. The energy landscape has a multi-valley
structure and ground-state configurations correspond to bifurcation points of
the valleys. In the high-field region, the shear modulus becomes independent of
field and its anisotropy dependence is given by .Comment: 4 pages, 7 figures (2 gif figures not in the text); RevTe
Crossover behaviors in liquid region of vortex states above a critical point caused by point defects
Vortex states in high- superconductors with point defects are
studied by large-scale Monte Carlo simulations of the three-dimensional
frustrated XY model. A critical point is observed on the first-order phase
boundary between the vortex slush and vortex liquid phases. A step-like anomaly
of the specific heat is detected in simulations of finite systems, similar to
an experimental observation [F.~Bouquet {\it et al.}, Nature (London) {\bf
411}, 448 (2001)]. However, it diminishes with increasing system size, and the
number and size distribution of thermally-excited vortex loops show continuous
behaviors around this anomaly. Therefore, the present study suggests a
crossover rather than a thermodynamic phase transition above the critical
point.Comment: 4 pages, 9 eps figures, using RevTeX
Quantum Hopfield Model
The Hopfield model in a transverse field is investigated in order to clarify
how quantum fluctuations affect the macroscopic behavior of neural networks.
Using the Trotter decomposition and the replica method, we find that the
(the ratio of the number of stored patterns to the system
size)- (the strength of the transverse field) phase diagram of this
model in the ground state resembles the - phase diagram of the
Hopfield model quantitatively, within the replica-symmetric and static
approximations. This fact suggests that quantum fluctuations play quite similar
roles to thermal fluctuations in neural networks as long as macroscopic
properties are concerned.Comment: 11 pages, 1 compressed/uuencoded postscript figure, revte
Evidence of first-order transition between vortex glass and Bragg glass phases in high- superconductors with point pins: Monte Carlo simulations
Phase transition between the vortex glass and the Bragg glass phases in
high- superconductors in is studied by
Monte Carlo simulations in the presence of point pins. A finite latent heat and
a -function peak of the specific heat are observed, which clearly
indicates that this is a thermodynamic first-order phase transition. Values of
the entropy jump and the Lindemann number are consistent with those of melting
transitions. A large jump of the inter-layer phase difference is consistent
with the recent Josephson plasma resonance experiment of
BiSrCaCuO by Gaifullin {\it et al.}Comment: 4 pages, 5 Postscript figures, uses revtex.st
Critical nonequilibrium relaxation in the Swendsen-Wang algorithm in the Berezinsky-Kosterlitz-Thouless and weak first-order phase transitions
Recently we showed that the critical nonequilibrium relaxation in the
Swendsen-Wang algorithm is widely described by the stretched-exponential
relaxation of physical quantities in the Ising or Heisenberg models. Here we
make a similar analysis in the Berezinsky-Kosterlitz-Thouless phase transition
in the two-dimensional (2D) XY model and in the first-order phase transition in
the 2D Potts model, and find that these phase transitions are described
by the simple exponential relaxation and power-law relaxation of physical
quantities, respectively. We compare the relaxation behaviors of these phase
transitions with those of the second-order phase transition in the 3D and 4D XY
models and in the 2D -state Potts models for , and show that
the species of phase transitions can be clearly characterized by the present
analysis. We also compare the size dependence of relaxation behaviors of the
first-order phase transition in the 2D and Potts models, and propose
a quantitative criterion on "weakness" of the first-order phase transition.Comment: 4 pages, 6 figures, RevTeX
Cluster nonequilibrium relaxation in Ising models observed with the Binder ratio
The Binder ratios exhibit discrepancy from the Gaussian behavior of the
magnetic cumulants, and their size independence at the critical point has been
widely utilized in numerical studies of critical phenomena. In the present
article we reformulate the nonequilibrium relaxation (NER) analysis in cluster
algorithms using the -Binder ratio, and apply this scheme to the two-
and three-dimensional Ising models. Although the stretched-exponential
relaxation behavior at the critical point is not explicitly observed in this
quantity, we find that there exists a logarithmic finite-size scaling formula
which can be related with a similar formula recently derived in cluster NER of
the correlation length, and that the formula enables precise evaluation of the
critical point and the stretched-exponential relaxation exponent .
Physical background of this novel behavior is explained by the simulation-time
dependence of the distribution function of magnetization in two dimensions and
temperature dependence of obtained from magnetization in three
dimensions.Comment: 8 pages, 20 figures, RevTeX4.1 (revision only for format of figures