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

Abstract
Inelastic neutron scattering experiments on the Haldane-gap quantum antiferromagnet Ni(C5D14N2)2N3(PF6) are performed in magnetic fields below and above the critical field Hc at which the gap closes. Quasielastic neutron scattering is found for H>Hc, indicating topological excitations in the high-field phase.