Quantum magnetism and quantum phase transitions

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The properties of Haldane excitations and multi-particle states in the antiferromagnetic spin-1 chain compound CsNiCl

(2001)

Authors:

M Kenzelmann, RA Cowley, WJL Buyers, Z Tun, R Coldea, M Enderle
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Direct Measurement of the Spin Hamiltonian and Observation of Condensation of Magnons in the 2D Frustrated Quantum Magnet Cs2CuCl4

(2001)

Authors:

R Coldea, DA Tennant, K Habicht, P Smeibidl, C Wolters, Z Tylczynski
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Correlations and fluctuations in the 2D Heisenberg antiferromagnet

Journal of Magnetism and Magnetic Materials 236:1-2 (2001) 4-5

Authors:

HM Ronnow, DF McMorrow, A Harrison, ID Youngson, R Coldea, TG Perring, G Aeppli, O Syljuåsen

Abstract:

The correlations and fluctuations in Cu(DCOO)2·4D2O, which is a good physical realization of the 2D S = 1/2 Heisenberg antiferromagnet on a square lattice, have been measured by neutron scattering measurements. The quantum fluctuations cause a non-uniform renormalization of the spin-wave dispersion with a zone boundary dispersion of 7%, while the spin wave amplitude is reduced to 51±4% of its classical value. The temperature dependence of the correlation length, the spin-wave damping and the spin-wave softening agrees with theoretical predictions over a large temperature range. © 2001 Elsevier Science B.V. All rights reserved.
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Spin dynamics of the 2D spin 1/2 quantum antiferromagnet copper deuteroformate tetradeuterate (CFTD).

Phys Rev Lett 87:3 (2001) 037202

Authors:

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

Abstract:

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<
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Multiparticle states in the S = 1 chain system CsNiCl3.

Phys Rev Lett 87:1 (2001) 017201

Authors:

M Kenzelmann, RA Cowley, WJ Buyers, R Coldea, JS Gardner, M Enderle, DF McMorrow, SM Bennington

Abstract:

A continuum of magnetic states has been observed by neutron scattering from the spin-1 chain compound CsNiCl3 in its disordered gapped one-dimensional phase. Results using both triple-axis and time-of-flight spectrometers show that around the antiferromagnetic point Qc = pi, the continuum lies higher in energy than the Haldane gapped excitations. At 6 K the integrated intensity of the continuum is about 12(2)% of the total spectral weight. This result is considerably larger than the 1%-3% weight predicted by the nonlinear sigma model for the three-particle continuum.
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