HEISENBERG-MODEL ON THE (1) (5)-DEPLETED SQUARE LATTICE AND THE CAV4O9 COMPOUND/

We investigate the ground-state structure of the Heisenberg model on t he 1/5-depleted square lattice for arbitrary values of the first- and second-neighbor exchange couplings. By using a mean-field Schwinger-bo son approach we present a unified description of the rich ground-slate phase diagram, which includes the plaquette and dimer resonant-valenc e-bond phases, long- and short-range Neel orders, an incommensurate ph ase: and other magnetic orders with complex magnetic unit cells. We al so discuss some implications of our results for the experimental reali zation of this model in the CaV4O9 compound.