SPIN-1 ANTIFERROMAGNETIC INTERACTION IN THE COUPLED HEISENBERG-CHAINS

A 2 x L system of coupled spin-1/2 Heisenberg chains is studied in the framework of variational approach. An effective Hamiltonian is derive d explicitly in terms of two spin-1 degrees of freedom of a cluster of L sites. The spin gap is calculated numerically for the systems of tw o coupled chains with periodic boundary condition. Our results are clo se to that of the density matrix renormalization group study. It is su ggested that there exists a spin-1 antiferromagnetic interaction in su ch system. (C) 1997 Elsevier Science B.V.