Spin Dynamics in the Two-Dimensional Spin 1/2 Heisenberg Antiferromagnet
  We present low-temperature dynamic properties of the quantum two-dimensional antiferromagnetic Heisenberg model with spin S=1/2. The calculation of the dynamic correlation function is performed by combining a projection operator formalism and the modified spin-wave theory (MSW), which gives a gap in the dispersion relation for finite temperatures. The so calculated dynamic correlation function shows a double peak structure.We also obtain the spin-wave damping and compare our results to experimental data and to theoretical results obtained by other authors using different approaches. 
A. F. Albuquerque, A. S. T. Pires and M. E. Gouvea