Spin hamiltonians with resonating-valence-bond ground states

Quantum dimer models exhibit quantum critical points and liquid states when the ground state is the resonating-valence bond (RVB) state. We construct SU(2)-invariant spin-1/2 Hamiltonians with the same RVB ground state. The main technical obstacle overcome is the fact that different dimer configurations in the spin model are not orthogonal. We show that the physics depends on how dimers are related to the spins, and find a Hamiltonian that is likely to be quantum critical.