Quantum Monte Carlo Study of Metal-Insulator Transitions on the Honeycomb Lattice

We investigate the band insulator-metal-Mott insulator transitions in the ionic Hubbard model on the 12*12 honeycomb lattice at half filling using determinant quantum Monte Carlo method. The phase diagram as a function of interaction U and staggered potential Δ indicates that the metallic state develops only if the interaction value varys in a moderate range. The Mott insulator state is antiferromagnetic. The conductivity decreases as the lattice size increases in metallic phase. A qualitative contrast to results obtained using the dynamical mean field theory is made at the end.