7 research outputs found
Comment on "Anomalous Thermal Conductivity of Frustrated Heisenberg Spin Chains and Ladders"
In a recent letter [Phys. Rev. Lett. 89, 156603 (2002); cond-mat/0201300],
Alvarez and Gros have numerically analyzed the Drude weight for thermal
transport in spin ladders and frustrated chains of up to 14 sites and have
proposed that it remains finite in the thermodynamic limit. In this comment, we
argue that this conclusion cannot be sustained if the finite-size analysis is
taken to larger system sizes.Comment: One page REVTeX4, 1 figure. Published version (minor changes
Bond-impurity induced bound states in disordered spin-1/2 ladders
We discuss the effect of weak bond-disorder in two-leg spin ladders on the
dispersion relation of the elementary triplet excitations with a particular
focus on the appearance of bound states in the spin gap. Both the cases of
modified exchange couplings on the rungs and the legs of the ladder are
analyzed. Based on a projection on the single-triplet subspace, the
single-impurity and small cluster problems are treated analytically in the
strong-coupling limit. Numerically, we study the problem of a single impurity
in a spin ladder by exact diagonalization to obtain the low-lying excitations.
At finite concentrations and to leading order in the inter-rung coupling, we
compare the spectra obtained from numerical diagonalization of large systems
within the single-triplet subspace with the results of diagrammatic techniques,
namely low-concentration and coherent-potential approximations. The
contribution of small impurity clusters to the density of states is also
discussed.Comment: 9 pages REVTeX4 including 7 figures, final version; Fig. 5 modifie
Thermal conductivity of anisotropic and frustrated spin-1/2 chains
We analyze the thermal conductivity of anisotropic and frustrated spin-1/2
chains using analytical and numerical techniques. This includes mean-field
theory based on the Jordan-Wigner transformation, bosonization, and exact
diagonalization of systems with N<=18 sites. We present results for the
temperature dependence of the zero-frequency weight of the conductivity for
several values of the anisotropy \Delta. In the gapless regime, we show that
the mean-field theory compares well to known results and that the
low-temperature limit is correctly described by bosonization. In the
antiferromagnetic and ferromagnetic gapped regime, we analyze the temperature
dependence of the thermal conductivity numerically. The convergence of the
finite-size data is remarkably good in the ferromagnetic case. Finally, we
apply our numerical method and mean-field theory to the frustrated chain where
we find a good agreement of these two approaches on finite systems. Our
numerical data do not yield evidence for a diverging thermal conductivity in
the thermodynamic limit in case of the antiferromagnetic gapped regime of the
frustrated chain.Comment: 4 pages REVTeX4 including 6 figures; published version, main
modification: added emphasis that the data of our Fig. 3 point to a vanishing
of the thermal Drude weight in the thermodynamic limit in this cas
Non-dissipative thermal transport in the massive regimes of the XXZ chain
We present exact results on the thermal conductivity of the one-dimensional
spin-1/2 XXZ model in the massive antiferromagnetic and ferromagnetic regimes.
The thermal Drude weight is calculated by a lattice path integral formulation.
Numerical results for wide ranges of temperature and anisotropy as well as
analytical results in the low and high temperature limits are presented. At
finite temperature, the thermal Drude weight is finite and hence there is
non-dissipative thermal transport even in the massive regime. At low
temperature, the thermal Drude weight behaves as where is the one-spinon (respectively
one-magnon) excitation energy for the antiferromagnetic (respectively
ferromagnetic) regime.Comment: 16 page