58 research outputs found
Dispersion relations and speeds of sound in special sectors for the integrable chain with alternating spins
Based on our previous analysis \cite{doerfel3} of the anisotropic integrable
chain consisting of spins and we compare the dispersion relations
for the sectors with infinite Fermi zones. Further we calculate the speeds of
sound for regions close to sector borders, where the Fermi radii either vanish
or diverge, and compare the results.Comment: 11 pages, LaTeX2e, uses iopart.cls,graphicx.sty and psfrag.sty, 2
figure
Complete phase diagram for the integrable chain with alternating spins in the sectors with competing interactions
We investigate the anisotropic integrable spin chain consisting of spins
and by means of thermodynamic Bethe ansatz for the anisotropy
, where the analysis of the Takahashi conditions leads to a more
complicated string picture. We give the phase diagram with respect to the two
real coupling constants and , which contains a new region
where the ground state is formed by strings with infinite Fermi zones. In this
region the velocities of sound for the two physical excitations have been
calculated from the dressed energies. This leads to an additional line of
conformal invariance not known before.Comment: 13 pages, LaTeX, uses ioplppt.sty and epsfig.sty, figure 3 correcte
Non-commutative Euclidean structures in compact spaces
Based on results for real deformation parameter q we introduce a compact non-
commutative structure covariant under the quantum group SOq(3) for q being a
root of unity. To match the algebra of the q-deformed operators with necesarry
conjugation properties it is helpful to define a module over the algebra
genera- ted by the powers of q. In a representation where X is diagonal we show
how P can be calculated. To manifest some typical properties an example of a
one-di- mensional q-deformed Heisenberg algebra is also considered and compared
with non-compact case.Comment: Changed conten
Existence of the magnetization plateau in a class of exactly solvable Ising-Heisenberg chains
The mapping transformation technique is applied to obtain exact results for
the spin-1/2 and spin-S (S=1/2,1) Ising-Heisenberg antiferromagnetic chain in
the presence of an external magnetic field. Within this scheme, a field-induced
first-order metamagnetic transition resulting in multiplateau magnetization
curves, is investigated in detail. It is found that the scenario of the plateau
formation depends fundamentally on the ratio between Ising and Heisenbrg
interaction constants, as well as on the anisotropy strength of the XXZ
Heisenberg interaction.Comment: 16 pages, 10 figures, submitted to J. Phys: Condens. Matte
Ground State Structure and Low Temperature Behaviour of an Integrable Chain with Alternating Spins
In this paper we continue the investigation of an anisotropic integrable spin
chain, consisting of spins and , started in our paper
\cite{meissner}. The thermodynamic Bethe ansatz is analysed especially for the
case, when the signs of the two couplings and differ. For
the conformally invariant model () we have calculated heat
capacity and magnetic susceptibility at low temperature. In the isotropic limit
our analysis is carried out further and susceptibilities are calculated near
phase transition lines (at ).Comment: 22 pages, LaTeX, uses ioplppt.sty and PicTeX macro
Mixed Heisenberg Chains. I. The Ground State Problem
We consider a mechanism for competing interactions in alternating Heisenberg
spin chains due to the formation of local spin-singlet pairs. The competition
of spin-1 and spin-0 states reveals hidden Ising symmetry of such alternating
chains.Comment: 7 pages, RevTeX, 4 embedded eps figures, final versio
Ground state and low excitations of an integrable chain with alternating spins
An anisotropic integrable spin chain, consisting of spins and
, is investigated \cite{devega}. It is characterized by two real
parameters and , the coupling constants of the spin
interactions. For the case and the ground state
configuration is obtained by means of thermodynamic Bethe ansatz. Furthermore
the low excitations are calculated. It turns out, that apart from free magnon
states being the holes in the ground state rapidity distribution, there exist
bound states given by special string solutions of Bethe ansatz equations (BAE)
in analogy to \cite{babelon}. The dispersion law of these excitations is
calculated numerically.Comment: 16 pages, LaTeX, uses ioplppt.sty and PicTeX macro
Thermodynamics and conformal properties of XXZ chains with alternating spins
The quantum periodic XXZ chain with alternating spins is studied. The
properties of the related R-matrix and Hamiltonians are discussed. A compact
expression for the ground state energy is obtained. The corresponding conformal
anomaly is found via the finite-size computations and also by means of the
Bethe ansatz method. In the presence of an external magnetic field, the
magnetic susceptibility is derived. The results are also generalized to the
case of a chain containing several different spins.Comment: 28 pages, LaTeX2
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