Publications associated with Quantum Magnetism and Quantum Phase Transitions

Spin dynamics of the model 2D quantum antiferromagnet CFTD

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HM Ronnow, DF McMorrow, R Coldea, A Harrison, ID Youngson, TG Perring, G Aeppli, O Syljyasen, K Lefmann, C Rischel

The magnetic excitation spectrum in the two-dimensional (2D) S=1/2 Heisenberg antiferromagnet copper deuteroformate tetradeuterate (CFTD) has been measured for temperatures up to T\sim J/2, where J=6.31+-0.02 meV is the 2D exchange coupling. For T\ll J, a dispersion of the zone boundary energy is observed, which is attributed to a wavevector dependent quantum renormalization. At higher temperatures, spin-wave-like excitations persist, but are found to broaden and soften. By combining our data with numerical calculations, and with existing theoretical work, a consistent description of the behaviour of the model system is found over the whole temperature interval investigated.

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