Abstract
We study the dispersion of magnetic excitations in a Heisenberg antiferromagnetic chain of spin S=1 with exchange J and single-ion anisotropy D. Chains of length up to 18 sites are studied by a Lanczo¨s method. For the Haldane phase D<≊J we show that the gap at zero momentum and =1 is given by the sum of the gaps in the sectors =1 and =0 at momentum π. The transition region near D=J is likely to be reduced to an isolated point. Large-D perturbation theory is smoothly recovered as soon as D>2J. We discuss the implications for experiments on Ni( (NENP) as well as .
- Received 9 March 1992
DOI:https://doi.org/10.1103/PhysRevB.46.10854
©1992 American Physical Society