Spin Dynamics in the Square-Lattice Antiferromagnet

We apply the Schwinger boson mean-field theory to the square-lattice Heisenberg antiferromagnet at low temperatures. For spin we confirm the renormalized classical behavior of the correlation length ^-1 (T) without appealing to spin-wave theory. We also present a detailed calculation of the dynamical structure factor. A quasielastic peak is featured near q= (, ), while for |q- (, ) |, spin-wave ridges appear. The uniform susceptibility interpolates between spin-wave results at T=0 and the high-temperature series of Rushbrooke and Wood. Our theory is distinct from theories in which fermionic spinon excitations determine the low-temperature spin dynamics.