SPIN-WAVE EXCITATION-SPECTRA AND SPECTRAL WEIGHTS IN SQUARE LATTICE ANTIFERROMAGNETS

Using a recently developed method for calculating series expansions of the excitation spectra of quantum lattice models, we obtain the spin- wave spectra for square lattice, S=1/2 Heisenberg-Ising antiferromagne ts. The calculated spin-wave spectrum for the Heisenberg model is clos e to but noticeably different from a uniformly renormalized classical (large-S) spectrum with the renormalization for the spin-wave velocity of approximately 1.18. The relative weights of the single-magnon and multiple-magnon contributions to neutron-scattering spectra are obtain ed for wave vectors throughout the Brillouin zone.