Ground state properties of a spin-3/2 model on a decorated square lattice

We present the construction of an optimum ground state for a quantum spin-3 /2 antiferromagnet. The spins reside on a decorated square lattice, in whic h the basis consists of a plaquette of four sites. By using the vertex stat e model approach we generate the ground state from the same vertices as tho se used for the corresponding ground state on the hexagonal lattice. The pr operties of these two ground states are very similar. Particularly there is also a parameter-controlled phase transition from a disordered to a Neel o rdered phase. In the regime of this transition, ground state properties can be obtained from an integrable classical vertex model.