HALDANE-GAP IN COUPLED INFINITE-U HUBBARD CHAINS WITH POSITIVE HOPPING INTEGRAL

A three-chain coupled infinite-ii Hubbard model with positive hopping integral is studied using a degenerate perturbation theory. We find th at in the limit t' much less than t, where t' and t are the intrachain and interchain hopping integral, respectively, this system can be reg arded as a spin-1 antiferromagnetic Heisenberg chain when the hole con centration is 1/3. The ground state is a singlet state and there exist s a Haldane gap in the spectrum of this system.