Half-integer Mott-insulator phases in the imbalanced honeycomb lattice

Abstract

Using mean-field theory, we investigate the ground state properties of ultracold bosons loaded in a honeycomb lattice with on-site repulsive interactions and imbalanced nearest-neighbor hopping amplitudes. Taking into account correlations between strongly coupled neighboring sites through an improved Gutzwiller ansatz, we predict the existence of half-integer Mott-insulator phases, i.e. states with half-integer filling and vanishing compressibility. These insulating phases result from the interplay between quantum correlations and the topology of the honeycomb lattice, and could be easily addressed experimentally as they have clear signatures in momentum space.

Berry curvature of interacting bosons in a honeycomb lattice

“…Because of its remarkable low-energy electronic excitations, graphene has been the source of many key discoveries [26,27] which sparked a vivid research flow now reaching new territories as exemplified by ultracold atoms loaded in optical lattices [24,[28][29][30][31][32][33][34][35][36]. In particular, the tight-binding model on the honeycomb lattice or equivalently on the brick wall lattice is well known to exhibit a Berry curvature in its band structure [25,37,38], such that the anomalous Hall effect can be observed [5,39].…”