2-DIMENSIONAL QUANTUM HEISENBERG-ANTIFERROMAGNET - EFFECTIVE-HAMILTONIAN APPROACH TO THE THERMODYNAMICS

In this paper we present an extensive study of the thermodynamic prope rties of the two-dimensional quantum Heisenberg antiferromagnet on the square lattice; the problem is tackled by the pure-quantum self-consi stent harmonic approximation, preciously applied to quantum spin syste ms with easy-plane anisotropies, modeled to fit the peculiar features of an isotropic system. Internal energy, specific heat, correlation fu nctions, staggered susceptibility and correlation length are shown for different values of the spin, and compared with the available high-te mperature expansion and quantum Monte Carlo results, as well as with t he available experimental data.