SUSCEPTIBILITY AND TRIPLET EXCITATION SPECTRUM FOR CAV4O9 - 3RD-ORDERPERTURBATION EXPANSIONS

The uniform susceptibility and tripler excitation spectrum of the Heis enberg antiferromagnet on the one-fifth depleted square lattice are ca lculated using the third-order perturbation expansion method from the viewpoint of the weakly coupled meta-plaquette picture. Both the susce ptibility and tripler excitation spectrum data for CaV4O9 are simultan eously explained. The origin of the relatively large spin gap in this compound is discussed.