Doubled Moiré flat bands in double-twisted few-layer graphite

We study the electronic structure of double-twisted few-layer graphite (DTFLG), which consists of three few-layer graphites (FLGs), i.e., an ABA-stacked graphene multilayer, stacked with two twist angles. We consider two categories of DTFLG, the alternately and chirally twisted cases, according to the rotation direction of the two twist angles. We show that, once the middle FLG of DTFLG is not thinner than the trilayer, both types of DTFLG can remarkably host two pairs of degenerate Moiré flat bands (MFBs) at E F , twice that of the magic angle twisted bilayer graphene (TBG). The doubled MFBs of DTFLG lead to a doubled density of states (DOS) at the Fermi level E F , which implies much stronger correlation effects than TBG. The degeneracy of MFBs can be lifted by a perpendicular electric field, and the isolated MFBs have a nonzero valley Chern number. We also reveal the peculiar wave function patterns of the MFBs in DTFLG. Our results establish a new family of Moiré systems that have a much higher DOS at E F and thus possibly much stronger correlation effects.