  Haldane model is a noninteracting model for spinless fermions showing
nontrivial topological properties. Effect of the electron-electron interaction
on the topological phase poses an intriguing question. By means of the
Hartree-Fock mean field, the exact diagonalization and the constrained-path
Monte Carlo methods we mapped out the phase diagram of the interacting Haldane
model. It is found that interaction breaks down the topological phase and
drives the system into the charge-density-wave state. Sequence of the two
transitions depends on the strength of next-nearest-neighbor hopping. Many-body
Chern number and the charge excitation gap are used to characterize the
topological transition.
