2-DIMENSIONAL HUBBARD ANTIFERROMAGNET

The finite-temperature properties of the two-dimensional Hubbard antiferromagnet are studied in its magnetically disordered state. In the strong-coupling limit the spin-correlation length to one-loop level is obtained as xi/a approximately exp{[M(O)Z(c)pi/2]J/k(B)T}, the coefficient in the exponential exhibiting substantial (23%) reduction due to zero-point quantum spin fluctuations in the ground state. A systematic evaluation, to one-loop order, of this coefficient yields M(O)Z(c)pi/2 = 1.20 in excellent agreement with recent Monte Carlo results. A relaxation model for the spin-wave excitations is used to obtain the spin response in the disordered state. The integrated structure factor is evaluated and is shown to compare quantitatively with the neutron-scattering data for integrated intensity from constant-energy scans in La2CuO4.