First-order Néel-valence-bond-solid transition in S= 32 antiferromagnets

We study the transition between Néel and columnar valence-bond solid ordering in two-dimensional S=3/2 square lattice quantum antiferromagnets with SO(3) symmetry. According to the deconfined criticality scenario, this transition can be direct and continuous like the well-studied S=1/2 case. To study the global phase diagram, we work with four multi-spin couplings with full rotational symmetry, that are free of the sign-problem of quantum Monte Carlo. Exploring the phase diagram with quantum Monte Carlo simulations, we find that the phase transition between Néel and valence-bond solid is strongly first-order in the parts of the phase diagram that we have accessed.