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Phys. Rev. Lett. 94, 177202 (2005) [4 pages]

Spin Excitations in an Anisotropic Bond-Alternating Quantum S=1 Chain in a Magnetic Field: Contrast to Haldane Spin Chains

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M. Hagiwara1,*, L. P. Regnault2, A. Zheludev3, A. Stunault4, N. Metoki5, T. Suzuki6, S. Suga6, K. Kakurai5, Y. Koike5, P. Vorderwisch7, and J.-H. Chung8
1RIKEN (The Institute of Physical and Chemical Research), Wako, Saitama 351-0198, Japan
2CEA-Grenoble, DRFMC-SPSMS-MDN, 17 rue des Martyrs, 38054 Grenoble Cedex 9, France
3Condensed Matter Sciences Division, Oak Ridge National Laboratory, Oak Ridge, Tennessee 37831-6393, USA
4Institut Laue Langevin, 6 rue J. Horowitz, 38042 Grenoble Cedex 9, France
5JAERI, Advanced Science Research Center, Tokai, Ibaraki 319-1195, Japan
6Department of Applied Physics, Osaka University, Suita, Osaka 565-0871, Japan
7BENSC, Hahn-Meitner Institut, D-14109 Berlin, Germany
8NIST Center for Neutron Research, National Institute of Standards and Technology, Gaithersburg, Maryland 20899, USA, and Department of Materials Science and Engineering, University of Maryland, College Park, Maryland 20742, USA

Received 7 January 2005; published 4 May 2005

Inelastic neutron scattering experiments on the S=1 quasi-one-dimensional bond-alternating antiferromagnet Ni(C9D24N4)(NO2)ClO4 have been performed under magnetic fields below and above a critical field Hc at which the energy gap closes. Normal field dependence of Zeeman splitting of the excited triplet modes below Hc 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 q∥=π that is present in dimerized chains but absent in uniform ones. Above Hc, 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)].

© 2005 The American Physical Society

URL:
http://link.aps.org/doi/10.1103/PhysRevLett.94.177202
DOI:
10.1103/PhysRevLett.94.177202
PACS:
75.40.Gb, 75.10.Jm, 75.50.Ee

*Present address: KYOKUGEN, Osaka University, 1-3 Machikaneyama, Toyonaka, Osaka 560-8531, Japan.

 
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