MAGNON DAMPING IN THE 2-DIMENSIONAL QUANTUM HEISENBERG-ANTIFERROMAGNET AT SHORT WAVELENGTHS

Dyson-Maleev boson formalism is used to calculate magnon damping k in the two-dimensional quantum Heisenberg antiferromagnet at low temperatures T and for wavelengths short compared to the thermal de Broglie wavelength. From the evaluation of the second-order self-energy it is found that kT3Z(vk) as T0, where vk is the gradient of dispersion relation of free magnons. For k close to the boundary of the Brillouin zone, where vk is small, the function Z has the expansion Z(vk)=1+O(vk-2). For general vk, we have calculated Z numerically. Although there is no long-range order at any T 0, the staggered correlation length (T) is exponentially large as T0. It is shown explicitly in the present work that, at low temperatures, magnons with momentum k in the regime k-a(T/E)1/3 (where a is the lattice spacing and E is the energy of zone-boundary magnons) are well-defined quasiparticles. We present evidence to support the argument that this remains true as long as k-1. © 1990 The American Physical Society.