Flat-Band Magnetism and Half-Metallicity in Twisted Bilayer Graphene*

Evidence of flat-band magnetism and half-metallicity in compressed twisted bilayer graphene is provided with first-principles calculations. We show that dynamic band-structure engineering in twisted bilayer graphene is possible by controlling the chemical composition with extrinsic doping, the interlayer coupling strength with pressure, and the magnetic ordering with external electric field. By varying the rotational order and reducing the interlayer separation an unbalanced distribution of charge density results in the spontaneous apparition of localized magnetic moments without disrupting the structural integrity of the bilayer. Substitutional doping shifts the chemical potential of one spin distribution and leads to half-metallicity.