Phase diagram topology of the Haldane-Hubbard-Coulomb model

We study the phase diagram of the interacting spin-$1/2$ Haldane model with chiral phase $φ= π/2$ at half-filling. Both on-site and long-range Coulomb repulsive interactions (Haldane-Hubbard-Coulomb model) are considered. The problem with on-site interaction $U$ alone was addressed in the past by a variety of approximate and finite size methods that produced results in disagreement with each other both quantitatively and qualitatively. Here we employ the Diagrammatic Monte Carlo technique to accurately locate phase transition points to the topologically nontrivial phases in the $(Δ, U)$-plane, where $\pm Δ$ is the inversion symmetry breaking on-site energy, and establish that momentum dependence of self-energy cannot be neglected in the proper treatment. We also find that even modest long-range interactions, typically discarded in theoretical considerations, result in significant shifts of transition lines.