Spin supersolidity versus phase separation in frustrated antiferromagnets

Full text: Dimer-based antiferromagnets (AF) in a magnetic field are promising candidates for displaying new phases of bosonic matter, in particular spin supersolidity, a phase where both diagonal and off-diagonal order are present. The presence of supersolid phases has been demonstrated for unfrustrated Heisenberg models with a large Ising anisotropy using Quantum Monte Carlo simulations, and the current challenge is to find isotropic Heisenberg models in which such phases could be realized since isotropic interactions are more realistic for Mott insulators. In this work, we study the competition between phase separation and supersolidity in a frustrated spin-1/2 bilayer model using the Contractor Renormalization Group (CORE) to derive an effective bosonic model. This study reveals that supersolidity is present but limited to a parameter range not investigated so far and of possible experimental relevance. (author)