Abstract
Inelastic neutron scattering experiments on the quasi-one-dimensional bond-alternating antiferromagnet have been performed under magnetic fields below and above a critical field at which the energy gap closes. Normal field dependence of Zeeman splitting of the excited triplet modes below has been observed, but the highest mode is unusually small and smears out with increasing field. This can be explained by an interaction with a low-lying two magnon continuum at that is present in dimerized chains but absent in uniform ones. Above , we find only one excited mode, in stark contrast with three massive excitations previously observed in the structurally similar Haldane-gap material NDMAP [A. Zheludev et al., Phys. Rev. B 68, 134438 (2003)].
- Received 7 January 2005
DOI:https://doi.org/10.1103/PhysRevLett.94.177202
©2005 American Physical Society