Dynamics of the two-dimensional spin-1/2Heisenberg antiferromagnet: Exact results versus Schwinger-boson mean-field theory

Abstract

We present the first exact results for the T=0 dynamical structure factor of finite-sized two-dimensional square-lattice spin-(1/2 antiferromagnetic Heisenberg systems with up to 16 spins. Our results are compared to a recently proposed Schwinger boson mean-field theory. We find that the mean-field theory represents an excellent approximation to the exact spin excitation spectra at all allowed wave vectors and for all system sizes studied. We also determine the mean-field value for the T=0 staggered magnetization, $m^{\mathrm{MF}=0.306\mathrm{}}$, to be in excellent agreement with published Monte Carlo results.