EXACT GROUND-STATE OF THE HUBBARD-MODEL ON A DOUBLE-LAYER SQUARE LATTICE

A group of analytical wave functions is confirmed to be the ground sta te of a Hubbard model on a double-layer square lattice in the case of half-filling and in the case with one or two doped holes for a range o f parameters. The method is based on the variational principle, and no approximations are applied. In the case of half-filling, the ground s tate is a product of local pairs. In the case of one or two holes, the doped holes are freely moving in the above background. In both cases there exists a long-range order of the evenness and oddness with respe ct to the layer parity.