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1/S-expansion study of spin waves in a two-dimensional Heisenberg antiferromagnet

Jun-ichi Igarashi·Tatsuya Nagao
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Abstract

We study the effects of quantum fluctuations on excitation spectra in the two-dimensional Heisenberg antiferromagnet by means of the 1/S expansion. We calculate the spin-wave dispersion and the transverse dynamical structure factor up to the second order of 1/S in comparison with inelastic neutron scattering experiments. The spin-wave energy at momentum $(π,0)$ is found to be about 2% smaller than that at $(π/2,π/2)$ due to the second-order correction. In addition, we study the dimensional crossover from two dimensions to one dimension by weakening exchange couplings in one direction. It is found that the second-order correction becomes large with approaching the quasi-one dimensional situation and makes the spin-wave energy approach to the des Cloizeaux-Pearson boundary for $S=1/2$. The transverse dynamical structure factor is also calculated up to the second order of 1/S. It is shown that the intensity of spin-wave peak is strongly reduced while the intensity of three-spin-wave continuum becomes large and exceeds that of the spin-wave peak in the quasi-one dimensional situation.

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Jun-ichi Igarashi, Tatsuya Nagao. 2005-04-26. 1/S-expansion study of spin waves in a two-dimensional Heisenberg antiferromagnet. https://doi.org/10.1103/physrevb.72.014403

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