RELAXATION FUNCTION-THEORY OF THE QUANTUM SPIN-1 2 HEISENBERG ANTIFERROMAGNETS AT FINITE TEMPERATURES/

We develop a self-consistent correlation theory of the relaxation func tion to investigate the static and dynamic properties of the spin-1/2 nearest-neighbor Heisenberg antiferromagnet on a square lattice. Self- consistency between the static and dynamic variables is achieved and s ome rigorous sum rules are derived as constraints to determine the par ameters in the static susceptibility. The calculated static quantities such as the internal energy, uniform susceptibility, correlation leng th, and specific heat are in reasonable agreement with the quantum Mon te Carlo results at intermediate and high temperatures. In addition, t he dynamic properties including the dynamic susceptibility, dynamic st ructure factor, and response function are also obtained at the same ti me, used ill connection with the experimental measurements of the nucl ear relaxation rates of the layered cuprates. This theory preserves th e spin rotational symmetry and the nonuniversal lattice correction and is valid for all wave vectors throughout the Brillouin zone. [S0163-1 829(97)03638-2].