paper

Exact two-spin dynamic structure factor of the one-dimensional s=1/2 Heisenberg-Ising antiferromagnet

arXiv:cond-mat/9712101 · doi:10.1103/PhysRevB.57.11429

Abstract

The exact 2-spinon part of the dynamic spin structure factor for the one-dimensional =1/2 model at =0 in the antiferromagnetically ordered phase is calculated using recent advances by Jimbo and Miwa in the algebraic analysis based on (infinite-dimensional) quantum group symmetries of this model and the related vertex models. The 2-spinon excitations form a 2-parameter continuum consisting of two partly overlapping sheets in -space. The spectral threshold has a smooth maximum at the Brillouin zone boundary and a smooth minimum with a gap at the zone center . The 2-spinon density of states has square-root divergences at the lower and upper continuum boundaries. For the 2-spinon transition rates, the two regimes (near the zone center) and (near the zone boundary) must be distinguished, where in the Heisenberg limit and in the Ising limit. The resulting 2-spinon part of is then square-root divergent at the spectral threshold and vanishes in a square-root cusp at the upper boundary. In the regime , by contrast, the 2-spinon transition rates have a smooth maximum inside the continuum and vanish linearly at either boundary. Existing perturbation studies have been unable to capture the physics of the regime . However, their line shape predictions for the regime are in good agreement with the new exact results if the anisotropy is very strong.

11 pages, 5 Postscript figures

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