Doping induced quantum bound states within the Haldane gap.

Abstract

Using the approach proposed by Zittartz and M\uller-Hartmann [Z. Phys. 232, 11 (1970)], we show explicitly that quantum bound states at the centre of the Haldane energy gap can be induced by doping in a spin-1 linear chain Heisenberg antiferromagnet. We calculate the dynamic structure factor $S(q,\ensuremath{\omega})$ due to these bound states and use it to interpret the recent neutron scattering experiments on doped ${\mathrm{Y}}_{2}{\mathrm{BaNiO}}_{5}$ [J. F. DiTusa et al., Phys. Rev. Lett. 73, 1857 (1994)].