Magnetic ordering tendencies in hexagonal-boron-nitride-bilayer-graphene moire structures

摘要

When hexagonal boron nitride (hBN) and graphene are aligned at zero or a small twist angle, a moire structure is formed due to the small lattice constant mismatch between the two structures. In this paper, we analyze magnetic ordering tendencies, driven by on-site Coulomb interactions, of encapsulated bilayer graphene (BG) forming a moire structure with one (hBN-BG) or both hBN layers (hBN-BG-hBN), using the random phase approximation. The calculations are performed in a fully atomistic Hubbard model that takes into account all n electrons of the carbon atoms in one moire unit cell. We analyze the charge neutral case and find that the dominant magnetic ordering instability is uniformly antiferromagnetic. Furthermore, at low temperatures, the critical Hubbard interaction U_c required to induce magnetic order is slightly larger in those systems where the moire structure has caused a band gap opening in the noninteracting picture, although the difference is less than 6%. Mean-field calculations are employed to estimate how such an interaction-induced magnetic order may change the observable single-particle gap sizes.