Magnetism near half-filling of a Van Hove singularity in twisted graphene bilayer

Abstract

Twisted graphene bilayers (TGBs) with slight twist angle always have low-energy Van Hove singularities (VHSs) that are strongly localized around AA-stacked regions of the moir\'e pattern. The localized VHSs are strongly related to novel correlated quantum states, such as Mott-like insulating phase and unconventional superconductivity, observed in the slightly TGBs. Here we studied the electronic properties of a TGB with $\ensuremath{\theta}\ensuremath{\sim}1.{64}^{\ensuremath{\circ}}$ and demonstrated that a VHS splits into two spin-polarized states flanking the Fermi energy when the VHS is close to the Fermi level. Such a result indicates that localized magnetic moments emerge in the AA-stacked regions of the TGB. Since the low-energy VHSs can be reached in slightly TGBs, our result therefore provides a facile direction to realize novel quantum phases in graphene system.