241 research outputs found
Field-induced incommensurate order for the quasi-one-dimensional XXZ model in a magnetic field
We investigate phase transitions of the quasi-one-dimensional XXZ model in a
magnetic field, using the bosonization combined with the mean field treatment
of the inter-chain interaction. We then find that the field induced
incommensurate order is certainly realized in the low field region, while the
transverse staggered order appears in the high field region. On the basis of
the result, we discuss the field-induced phase transition recently observed for
BaCo2V2O8.Comment: 6 pages, 3 figures, to appear in PR
Corner Transfer Matrix Renormalization Group Method Applied to the Ising Model on the Hyperbolic Plane
Critical behavior of the Ising model is investigated at the center of large
scale finite size systems, where the lattice is represented as the tiling of
pentagons. The system is on the hyperbolic plane, and the recursive structure
of the lattice makes it possible to apply the corner transfer matrix
renormalization group method. From the calculated nearest neighbor spin
correlation function and the spontaneous magnetization, it is concluded that
the phase transition of this model is mean-field like. One parameter
deformation of the corner Hamiltonian on the hyperbolic plane is discussed.Comment: 4 pages, 5 figure
Kramers-Wannier Approximation for 3D Ising Model
We investigate the Kramers-Wannier approximation for the three-dimensional
(3D) Ising model. The variational state is represented by an effective 2D Ising
model, which contains two variational parameters. We numerically calculate the
variational partition function using the corner transfer matrix renormalization
group (CTMRG) method, and find its maximum with respect to the variational
parameters. The calculated transition point is only 1.5%
less than the true ; the result is better than that obtained by the
corner transfer tensor renormalization group (CTTRG) approach. The calculated
phase transition is mean-field like.Comment: 7 pages, 4 figures, submitted to Prog. Theor. Phy
Spin-Chirality Separation and S_3-Symmetry Breakings in the Magnetization Plateau of the Quantum Spin Tube
We study the magnetization plateau state of the three-leg spin-1/2 tube in
the strong rung coupling region, where S_3-symmetry breakings and low-energy
chirality degree of freedom play crucial roles. On the basis of the effective
chirality model and density matrix renormalization group, we clarify that, as
the leg coupling increases, the chirality liquid with gapless non-magnetic
excitations, the spin imbalance phase and the vector-spin-chirality ordered
phase emerge without closing the plateau spin gap. The relevance of these
results to experiments is also discussed.Comment: 6 pages, 6 figures, detailed results of the spin imbalance state are
adde
On calculation of vector spin chirality for zigzag spin chains
We calculate the vector spin chirality for zigzag spin chains having
U(1) symmetry, using the density matrix renormalization group combined with
unitary transformation. We then demonstrate the occurrence of the chiral order
for the zigzag XY chain and discuss the associated phase transition. The
results are consistent with the analysis based on the bosonization and the long
distance behaviour of the chirality correlation function. For the
zigzag Heisenberg chain in a magnetic field, we also verify the chiral order
that is predicted by the effective field theory and the chirality correlation
function, and then determine its magnetic phase diagram.Comment: 7 pages, 9 figures, accepted for publication in J. Phys. Soc. Jp
Fractional S^z excitation and its bound state around the 1/3 plateau of the S=1/2 Ising-like zigzag XXZ chain
We present the microscopic view for the excitations around the 1/3 plateau
state of the Ising-like zigzag XXZ chain. We analyze the low-energy excitations
around the plateau with the degenerating perturbation theory from the Ising
limit, combined with the Bethe-form wave function. We then find that the
domain-wall particles carrying and its bound state of describe well the low-energy excitations around the 1/3 plateau state. The
formation of the bound state of the domain-walls clearly provides the
microscopic mechanism of the cusp singularities and the even-odd behavior in
the magnetization curve.Comment: 13 pages, 15 figure
Self-Consistent Tensor Product Variational Approximation for 3D Classical Models
We propose a numerical variational method for three-dimensional (3D)
classical lattice models. We construct the variational state as a product of
local tensors, and improve it by use of the corner transfer matrix
renormalization group (CTMRG), which is a variant of the density matrix
renormalization group (DMRG) applied to 2D classical systems. Numerical
efficiency of this approximation is investigated through trial applications to
the 3D Ising model and the 3D 3-state Potts model.Comment: 12 pages, 6 figure
Magnetic phase diagram of the S=1/2 antiferromagnetic zigzag spin chain in the strongly frustrated region: cusp and plateau
We determine the magnetic phase diagram of the antiferromagnetic(AF) zigzag
spin chain in the strongly frustrated region, using the density matrix
renormalization group method. We find the magnetization plateau at 1/3 of the
full moment accompanying the spontaneous symmetry breaking of the translation,
the cusp singularities above and/or below the plateau, and the even-odd effect
in the magnetization curve. We also discuss the formation mechanisms of the
plateau and cusps briefly.Comment: 4 pages, 8 figures, revised version, to appear in J.Phys.Soc.Jp
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