Featureless and nonfractionalized Mott insulators on the honeycomb lattice at 1/2 site filling

Significance Symmetries are increasingly shown to play various key roles determining the possible phases in condensed matter systems. We study bosonic particles (including electron Cooper pairs) living on the vertices of a honeycomb lattice at a density of 1/2 per site. Here the honeycomb symmetries forbid the usual fermionic band insulating state, and the conventional Mott (“strongly interacting”) insulator involves a whole number of particles frozen on each site, suggesting that featureless (fully symmetric) insulators might not exist in this system. Nevertheless, we explicitly construct quantum states and demonstrate that they are examples of featureless insulators on the honeycomb lattice at 1/2 site filling, with a procedure generalizing to lattices with symmorphic symmetry groups.