Frustrated Heisenberg antiferromagnet on the honeycomb lattice: A candidate for deconfined quantum criticality

We study the ground-state (gs) phase diagram of the frustrated spin-12 J₁-J₂-J₃ antiferromagnet with J ₂=J₃=κJ₁ on the honeycomb lattice using coupled-cluster theory and exact diagonalization methods. We present results for the gs energy, magnetic order parameter, spin-spin correlation function, and plaquette valence-bond crystal (PVBC) susceptibility. We find a Néel antiferromagnetic (AFM) phase for κ<κ_c1≈0.47, a collinear striped AFM phase for κ>κ_c2≈0.60, and a paramagnetic PVBC phase for κ_c1κκ_c2. The transition at κ_c2 appears to be of first-order type, while that at κ_c1 is continuous. Since the Néel and PVBC phases break different symmetries our results favor the deconfinement scenario for the transition at κ_c1.