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

D. C. Dender·P. R. Hammar·Daniel H. Reich·C. Broholm·G. Aeppli
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Abstract

Neutron scattering from copper benzoate, Cu(C6D5COO)2 3D2O, 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 wavevectors q=π+- dq(H) where dq(H) ~ 2 πM(H)/gμ_B as predicted by Bethe ansatz and spinon descriptions of the S = 1/2 chain. Unexpected was a field-induced energy gap $Δ(H) \propto H^α$, where $α= 0.65(3)$ as determined from specific heat measurements. At H = 7 T (gμ_B H/J = 0.52), the magnitude of the gap varies from 0.06 - 0.3 J depending on the orientation of the applied field.

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D. C. Dender, P. R. Hammar, Daniel H. Reich, C. Broholm, G. Aeppli. 1997-04-04. Direct Observation of Field-Induced Incommensurate Fluctuations in a One-Dimensional S=1/2 Antiferromagnet. https://doi.org/10.1103/physrevlett.79.1750

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