We introduce twisted trilayer graphene (tTLG) with two independent twist angles as an ideal system for the precise tuning of the electronic interlayer coupling to maximize the effect of correlated behaviors. As established by experiment and theory in the related twisted bilayer graphene system, van Hove singularities (VHS) in the density of states can be used as a proxy of the tendency for correlated behaviors. To explore the evolution of VHS in the twist-angle phase space of tTLG, we present a general low-energy electronic structure model for any pair of twist angles. We show that the basis of the model has infinite dimensions even at a finite energy cutoff and that no Brillouin zone exists even in the continuum limit. Using this model, we demonstrate that the tTLG system exhibits a wide range of magic angles at which VHS merge and that the density of states has a sharp peak at the charge-neutrality point through two distinct mechanisms: The incommensurate perturbation of twisted bilayer graphene's flatbands or the equal hybridization between two bilayer moiré superlattices.
Bibliographical noteFunding Information:
We thank Ke Wang, Xi Zhang, Kan-Ting Tsai, Francisco Guinea, Philip Kim, and Paul Cazeaux for helpful discussions. This work was supported by the STC Center for Integrated Quantum Materials, NSF Grant No. DMR-1231319, ARO MURI Grant No. W911NF-14-0247, and NSF DMREF Grant No. 1922165. Calculations were performed on the Odyssey cluster supported by the FAS Division of Science, Research Computing Group at Harvard University.
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