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Phys. Rev. Lett. 79, 1750–1753 (1997)

Direct Observation of Field-Induced Incommensurate Fluctuations in a One-Dimensional S = 1/2 Antiferromagnet

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D. C. Dender1, P. R. Hammar1, Daniel H. Reich1, C. Broholm1,2, and G. Aeppli3
1Department of Physics and Astronomy, The Johns Hopkins University, Baltimore, Maryland 21218
2National Institute of Standards and Technology, Gaithersburg, Maryland 20899
3NEC Research Institute, 4 Independence Way, Princeton, New Jersey 08540

Received 31 March 1997; published in the issue dated 1 September 1997

Neutron scattering from copper benzoate, Cu(C6D5COO)2̇3D2O, provides the first direct experimental evidence for field-dependent incommensurate low energy modes in a one-dimensional spin S = 1/2 antiferromagnet. Soft modes occur for wave vectors q̃ = π±δq̃(H), where δq̃(H)≈2πM(H)/gμB as predicted by Bethe ansatz and spinon descriptions of the S = 1/2 chain. Unexpected was a field-induced energy gap Δ(H)∝Hα, where α = 0.65(3) as determined from specific heat measurements. At H = 7T ( gμBH/J = 0.52), the magnitude of the gap varies from 0.06Jto0.3J depending on the orientation of the applied field.

© 1997 The American Physical Society

URL:
http://link.aps.org/doi/10.1103/PhysRevLett.79.1750
DOI:
10.1103/PhysRevLett.79.1750
PACS:
75.10.Jm, 75.25.+z, 75.50.Ee
 
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