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Evolution of spin excitations in a gapped antiferromagnet from the quantum to the high-temperature limit

M. Kenzelmann·R. A. Cowley·W. J. L. Buyers·R. Coldea·M. Enderle·D. F. McMorrow
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Abstract

We have mapped from the quantum to the classical limit the spin excitation spectrum of the antiferromagnetic spin-1 Heisenberg chain system CsNiCl3 in its paramagnetic phase from T=5 to 200K. Neutron scattering shows that the excitations are resonant and dispersive up to at least T=70K, but broaden considerably with increasing temperature. The dispersion flattens out with increasing temperature as the resonance energy Delta at the antiferromagnetic wave-vector increases and the maximum in the dispersion decreases. The correlation length xi between T=12 and 50K is in agreement with quantum Monte Carlo calculations. xi is also consistent with the single mode approximation, suggesting that the excitations are short-lived single particle excitations. Below T=12K where three-dimensional spin correlations are important, xi is shorter than predicted and the experiment is not consistent with the random phase approximation for coupled quantum chains. At T=200K, the structure factor and second energy moment of the excitation spectrum are in excellent agreement with the high-temperature series expansion.

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M. Kenzelmann, R. A. Cowley, W. J. L. Buyers, R. Coldea, M. Enderle, D. F. McMorrow. 2001-12-11. Evolution of spin excitations in a gapped antiferromagnet from the quantum to the high-temperature limit. https://doi.org/10.1103/physrevb.66.174412

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