We study high-field magnon dynamics and examine the dynamical structure factor in the quasi-two-dimensional tetragonal Heisenberg antiferromagnet with interlayer coupling corresponding to realistic materials. Within spin-wave theory, we show that a nonzero interlayer coupling mitigates singular corrections to the excitation spectrum occurring in the high-field regime that would otherwise require a self-consistent approach beyond the $1/S$ approximation. For the fields between the threshold for decays and saturation field, we observe widening of the two-magnon sidebands with significant shifting of the spectral weight away from the quasiparticle peak. We find spectrum broadening throughout large regions of the Brillouin zone, dramatic redistributions of spectral weight to the two-magnon continuum, two-peak structures, and other features clearly unlike conventional single-particle peaks.

• Received 5 March 2012

DOI:https://doi.org/10.1103/PhysRevB.85.184405