# Spin excitations and sum rules in the Heisenberg antiferromagnet.

@article{Stringari1994SpinEA, title={Spin excitations and sum rules in the Heisenberg antiferromagnet.}, author={Stringari}, journal={Physical review. B, Condensed matter}, year={1994}, volume={49 10}, pages={ 6710-6717 } }

Various bounds for the energy of collective excitations in the Heisenberg antiferromagnet are presented and discussed using the formalism of sum rules. We show that the Feynman approximation significantly overestimates (by about 30% in the S=1/2 square lattice) the spin velocity due to the non-negligible contribution of multiple magnons to the energy-weighted sum rule. We also discuss a different, Goldstone-type bound depending explicitly on the order parameter (staggered magnetization). This…

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