5 research outputs found
Spinons, Solitons and Magnons in One-dimensional Heisenberg-Ising Antiferromagnets
We calculate the excitation spectra for the one- Heisenberg-Ising
antiferromagnets by expansions around the Ising limit. For , the
calculated expansion coefficients for the spinon-spectra agree term by term
with the solution of Johnson and McCoy. For , the solitons become gapless
before the Heisenberg limit is reached, signalling a transition to the Haldane
phase. By applying a staggered field we calculate the one-magnon spectra for
the Heisenberg chain. For the quantum renormalization of the
spin-wave spectra is calculated to be approximately .Comment: 4 pages, RevTex, 3 postscript figures, Latex file and figures have
been uuencode
Large-Scale Numerical Evidence for Bose Condensation in the S=1 Antiferromagnetic Chain in a Strong Field
Using the recently proposed density matrix renormalization group technique we
show that the magnons in the S=1 antiferromagnetic Heisenberg chain effectively
behaves as bosons that condense at a critical field h_c.Comment: 12 pages, REVTEX 3.0, 3 postscript figures appended, UBCTP-93-00
S(k) for Haldane Gap Antiferromagnets: Large-scale Numerical Results vs. Field Theory and Experiment
The structure function, S(k), for the s=1, Haldane gap antiferromagnetic
chain, is measured accurately using the recent density matrix renormalization
group method, with chain-length 100. Excellent agreement with the nonlinear
model prediction is obtained, both at where a single
magnon process dominates and at where a two magnon process
dominates. We repeat our calculation with crystal field anisotropy chosen to
model NENP, obtaining good agreement with both field theory predictions and
recent experiments. Correlation lengths, gaps and velocities are determined for
both polarizations.Comment: 11 pages, 3 postscript figures included, REVTEX 3.0, UBCTP-93-02
Equal Time Correlations in Haldane Gap Antiferromagnets
The antiferromagnetic Heisenberg chain both with and without single ion
anisotropy is studied. Using the recently proposed density matrix
renormalization group technique we calculate the energy gaps as well as several
different correlation functions. The two gaps, ,
along with associated correlation lengths and velocities are determined. The
numerical results are shown to be in good agreement with theoretical
predictions derived from the nonlinear sigma model and a free boson model. We
also study the excitations that occur at the ends of open chains; in
particular we study the behavior associated with open boundary conditions,
using a model of spins coupled to the free bosons.Comment: 32 pages, uufiles encoded REVTEX 3.0, 19 postscript figures included,
UBCTP-93-02
Properties of Haldane excitations and multiparticle states in the antiferromagnetic spin-1 chain compound CsNiCl<sub>3</sub>
We report inelastic time-of-flight and triple-axis neutron scattering
measurements of the excitation spectrum of the coupled antiferromagnetic spin-1
Heisenberg chain system CsNiCl3. Measurements over a wide range of wave-vector
transfers along the chain confirm that above T_N CsNiCl3 is in a
quantum-disordered phase with an energy gap in the excitation spectrum. The
spin correlations fall off exponentially with increasing distance with a
correlation length xi=4.0(2) sites at T=6.2K. This is shorter than the
correlation length for an antiferromagnetic spin-1 Heisenberg chain at this
temperature, suggesting that the correlations perpendicular to the chain
direction and associated with the interchain coupling lower the single-chain
correlation length. A multi-particle continuum is observed in the
quantum-disordered phase in the region in reciprocal space where
antiferromagnetic fluctuations are strongest, extending in energy up to twice
the maximum of the dispersion of the well-defined triplet excitations. We show
that the continuum satisfies the Hohenberg-Brinkman sum rule. The dependence of
the multi-particle continuum on the chain wave-vector resembles that of the
two-spinon continuum in antiferromagnetic spin-1/2 Heisenberg chains. This
suggests the presence of spin-1/2 degrees of freedom in CsNiCl3 for T < 12K,
possibly caused by multiply-frustrated interchain interactions.Comment: 15 pages revtex, submitted to PR