We calculate dynamical structure factors of the $S=1$ bond-alternating Heisenberg chain with a single-ion anisotropy in transverse magnetic fields, using a continued fraction method based on the Lanczos algorithm. In the Haldane-gap phase and the dimer phase, dynamical structure factors show characteristic field dependence. Possible interpretations are discussed in the viewpoint of the field dependence of the excitation continuum. The numerical results are in qualitative agreement with recent results for inelastic neutron-scattering experiments on the $S=1$ bond-alternating Heisenberg-chain compound $\mathrm{Ni}\left({\mathrm{C}}_9{\mathrm{D}}_{24}{\mathrm{N}}_4\right)\left(\mathrm{N}{\mathrm{O}}_2\right)\mathrm{Cl}{\mathrm{O}}_4$ and the $S=1$ Haldane-gap compound $\mathrm{Ni}{\left({\mathrm{C}}_5{\mathrm{D}}_{14}{\mathrm{N}}_2\right)}_2{\mathrm{N}}_3\left(\mathrm{P}{\mathrm{F}}_6\right)$ in transverse magnetic fields.

• Received 9 May 2005

DOI:https://doi.org/10.1103/PhysRevB.72.014434