Quasielastic Neutron Scattering in the High-Field Phase of a Haldane Antiferromagnet

Abstract

Inelastic neutron scattering experiments on the Haldane-gap quantum antiferromagnet $\mathrm{Ni}({\mathrm{C}}_{5}{\mathrm{D}}_{14}{\mathrm{N}}_{2}{)}_{2}\ensuremath{-}{\mathrm{N}}_{3}({\mathrm{PF}}_{6})$ are performed in magnetic fields below and above the critical field ${H}_{c}$ at which the gap closes. Quasielastic neutron scattering is found for $H>{H}_{c}$, indicating topological excitations in the high-field phase.