4,576 research outputs found
Ground-State Phase Diagram of the Two-Dimensional Extended Bose-Hubbard Model
We investigate the ground-state phase diagram of the soft-core Bose-Hubbard
model with the nearest-neighbor repulsion on a square lattice by using an
unbiased quantum Monte Carlo method. In contrast to the previous study[P.
Sengupta {\it et. al.}, Phys. Rev. Lett. {\bf 94}, 207202 (2005)], we present
the ground-state phase diagrams up to large hopping parameters. As a result, in
addition to the known supersolid above half-filling, we find supersolid even
below and at half-filling for large hopping parameters. Furthermore, for the
strong nearest-neighbor repulsion, we show that the supersolid phase occupies a
remarkably broad region in the phase diagram. The results are in qualitative
agreement with that obtained by the Gutzwiller mean-field approximation[M.
Iskin, Phys. Rev. A {\bf 83}, 051606(R) (2011) and T. Kimura, Phys. Rev. A {\bf
84}, 063630 (2011)]
Spin-chirality decoupling in the one-dimensional Heisenberg spin glass with long-range power-law interactions
We study the issue of the spin-chirality decoupling/coupling in the ordering
of the Heisenberg spin glass by performing large-scale Monte Carlo simulations
on a one-dimensional Heisenberg spin-glass model with a long-range power-law
interaction up to large system sizes. We find that the spin-chirality
decoupling occurs for an intermediate range of the power-law exponent.
Implications to the corresponding -dimensional short-range model is
discussed.Comment: 5 pages, 4 figures, to appear in Physical Review Letter
Optimal design of injection mold for plastic bonded magnet
The optimal design of an injection mold for producing a stronger multipole magnet is carried out using the finite element method and the direct search method. It is shown that the maximum flux density in the cavity obtained by the optimal design is about 2.6 times higher than that of the initial shape determined empirically. 3-D analysis of the nonlinear magnetic field in the injection mold with complicated structure is also carried out. The calculated flux distribution on the cavity surface is in good agreement with the measured one</p
Accessing the dynamics of large many-particle systems using Stochastic Series Expansion
The Stochastic Series Expansion method (SSE) is a Quantum Monte Carlo (QMC)
technique working directly in the imaginary time continuum and thus avoiding
"Trotter discretization" errors. Using a non-local "operator-loop update" it
allows treating large quantum mechanical systems of many thousand sites. In
this paper we first give a comprehensive review on SSE and present benchmark
calculations of SSE's scaling behavior with system size and inverse
temperature, and compare it to the loop algorithm, whose scaling is known to be
one of the best of all QMC methods. Finally we introduce a new and efficient
algorithm to measure Green's functions and thus dynamical properties within
SSE.Comment: 11 RevTeX pages including 7 figures and 5 table
Crossovers in the Two Dimensional Ising Spin Glass with ferromagnetic next-nearest-neighbor interactions
By means of extensive computer simulations we analyze in detail the two
dimensional Ising spin glass with ferromagnetic next-nearest-neighbor
interactions. We found a crossover from ferromagnetic to ``spin glass'' like
order both from numerical simulations and analytical arguments. We also present
evidences of a second crossover from the ``spin glass'' behavior to a
paramagnetic phase for the largest volume studied.Comment: 19 pages with 9 postscript figures also available at
http://chimera.roma1.infn.it/index_papers_complex.html. Some changes in
captions of figures 1 and
Reply to Comment on "Quantum Phase Transition of Randomly-Diluted Heisenberg Antiferromagnet on a Square Lattice"
This is a reply to the comment by A. W. Sandvik (cond-mat/0010433) on our
paper Phys. Rev. Lett. 84, 4204 (2000). We show that his data do not conflict
with our data nor with our conclusions.Comment: RevTeX, 1 page; Revised versio
Chaos in a Two-Dimensional Ising Spin Glass
We study chaos in a two dimensional Ising spin glass by finite temperature
Monte Carlo simulations. We are able to detect chaos with respect to
temperature changes as well as chaos with respect to changing the bonds, and
find that the chaos exponents for these two cases are equal. Our value for the
exponent appears to be consistent with that obtained in studies at zero
temperature.Comment: 4 pages, LaTeX, 4 postscript figures included. The analysis of the
data is now done somewhat differently. The results are consistent with the
chaos exponent found at zero temperature. Additional papers of PY can be
obtained on-line at http://schubert.ucsc.edu/pete
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