Interaction-induced insulating states in multilayer graphenes

We explore the electronic ground states of Bernal-stacked multilayer graphenes using the Hartree-Fock mean-field approximation and the full-parameter band model. We find that the electron-electron interaction tends to open a band gap in multilayer graphenes from bilayer to eight-layer, while the nature of the insulating ground state sensitively depends on the band parameter γ2, which is responsible for the semimetallic nature of graphite. In four-layer graphene, particularly, the ground state assumes an odd-spatial-parity staggered phase at γ2=0, while an increasing, finite value of γ2 stabilizes a different state with even parity, where the electrons are attracted to the top layer and the bottom layer. The two phases are topologically distinct insulating states with different Chern numbers, and they can be distinguished by spin or valley Hall conductivity measurements. Multilayers with more than five layers also exhibit similar ground states with potential minima at the outermost layers, although the opening of a gap in the spectrum as a whole is generally more difficult than in four-layer because of a larger number of energy bands overlapping at the Fermi energy.