Dynamical structure factors of S=1 bond-alternating Heisenberg chains
Abstract
We calculate the dynamical structural factor of the S=1 bond-alternating Heisenberg chain. In the Haldane phase, the lowest excited states form the lower edge of the multimagnon continuum in 0 ≤ q ≤ qc and the one-magnon mode in qc ≤ q ≤ π. As the system approaches the gapless point, qc shifts towards q=π and the largest integrated intensity of the one-magnon mode is decreased. In the singlet-dimer phase, the one-magnon mode appears in 0 ≤ q ≤ qc. As the bond-alternation becomes strong, qc shifts towards q=π. In the antiferromagnetic-ferromagnetic bond-alternation region with a strong ferromagnetic coupling, the lowest excited states form the lower edge of the multimagnon continuum in 0 ≤ q ≤ 0.2π and 0.8π ≤ q ≤ π, and the one-magnon mode appears in 0.2π<q<0.8π. The largest integrated intensity of the one-magnon mode is 93%, which is slightly smaller than that in the S=1 Haldane-gap system. We further discuss the dynamical structural factor in connection with the inelastic neutron-scattering experiments.
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