CRITICAL-BEHAVIOR OF THE QUANTUM SPIN-1 2 ANISOTROPIC HEISENBERG-MODEL/

A two-step renormalization group approach - a decimation followed by a n effective field renormalization group (EFRG) - is proposed in this w ork to study the critical behavior of the quantum spin-1/2 anisotropic Heisenberg model. The new method is illustrated by employing approxim ations in which clusters with one. two and three spins are used. The v alues of the critical parameter and critical exponent, in two- and thr ee-dimensional lattices, for the Ising and isotropic Heisenberg limits are calculated and compared with other renormalization group approach es and exact (or series) results. (C) 1998 Elsevier Science B.V. All r ights reserved.