The extended Hubbard model on a honeycomb lattice

Abstract

We investigate the phase diagram of the extended Hubbard model on a half-filled honeycomb lattice through determinant quantum Monte Carlo simulations. At zero temperature, the repulsive Hubbard model undergo es a transition to an antiferromagnetic state only for sufficiently strong on-site coupling, U. However, the inclusion of a repulsive extended interaction, V , between fermions in nearest-neighbor orbitals induces a charge-ordered phase. For attractive interactions, we also identify superconducting and phase-separated phases. We have determined a complete phase diagram with the aid of structure factors associated with various orderings, combined with measurements of double occupancy and the average sign of fermionic determinants. We have established that the semi-metallic phase forms a zone from which ordered phases are excluded, preventing the stabilization of a superconducting phase with d-wave symmetry, i.e.,only s-wave pairing is allowed.