Spin-Peierls states of quantum antiferromagnets on the CaV4O9 lattice

We discuss the quantum paramagnetic phases of Heisenberg antiferromagnets on the 1/5-depleted square lattice found in CaV4O9. The possible phases of the quantum dimer model on this lattice are obtained by a mapping to a quantum-mechanical height model. In addition to the ''decoupled'' phases found earlier, we find a possible intermediate spin-Peierls phase with spontaneously broken lattice symmetry. Experimental signatures of the different quantum paramagnetic phases ate discussed.