Publications associated with Quantum Magnetism and Quantum Phase Transitions

Spin dynamics of the 2D spin 1/2 quantum antiferromagnet copper deuteroformate tetradeuterate (CFTD).

Phys Rev Lett 87 (2001) 037202-

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

The magnetic excitation spectrum in the two-dimensional (2D) S = 1/2 Heisenberg antiferromagnet copper deuteroformate tetradeuterate has been measured for temperatures up to T approximately J/2, where J = 6.31+/-0.02 meV is the 2D exchange coupling. For T<J, a dispersion of the zone boundary energy is observed, which is attributed to a wave vector dependent quantum renormalization. At higher temperatures, spin-wavelike 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 behavior of the model system is found over the whole temperature interval investigated.

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