THE SPIN STIFFNESS AND THE TRANSVERSE SUSCEPTIBILITY OF THE HALF-FILLED HUBBARD-MODEL

The T = 0 spin stiffness rho(S) and the transverse susceptibility chi( perpendicular to) of the square lattice half-filled Hubbard model are calculated as a function of the Hubbard parameter ratio U/t by series expansions around the Ising limit. We find that the calculated spin st iffness, transverse susceptibility, and sublattice magnetization for t he Hubbard model smoothly approach the Heisenberg values for large U/t . The results are compared for different U/t with RPA and other numeri cal studies. The uniform susceptibility data indicate a crossover arou nd U/t approximate to 4 between weak-coupling (spin density wave) beha vior at small U and strong-coupling (Heisenberg) behavior at large U.