Magic angles and flat Chern bands in alternating-twist multilayer graphene system

摘要

Based on the effective continuum model,we study alternating-twist multilayer graphene system and emergence of magic angles and flat band topology.All the alternating-twist multilayer graphene system(from triple layers to few layers)are found to have flat bands at magic angles where the area of AA stacking equals n-fold(n is an integer)electron cyclotron area.From the pseudo-Landau-level representation,there is always an isolated Dirac band in the alternating-twist graphene system constructed by odd number of layers.Since each pair of flat bands can be perceived as the zeroth pseudo-Landau-levels in two dimensional Dirac fermions,electron in the flat band pair can feel a pseudo-magnetic field with the same magnitude but the opposite sign.Calculated Chern number for each flat band is+1(or-1)which can be tuned by twisting in the vicinity of magic angles or by gating.The concurrent appearance of strong correlation and band topology of flat bands in the alternating-twist multilayer graphene may pave an avenue for the new understanding of superconductivity observed in triple-layered graphene,and supply a new playground for realizing(quantum)anomalous Hall effect.