Electronic properties of twisted bilayer graphene suspended and encapsulated with hexagonal boron nitride

M Long and Z Zhan and PA Pantaleón and JA Silva-Guillén and F Guinea and SJ Yuan, PHYSICAL REVIEW B, 107, 115140 (2023).

DOI: 10.1103/PhysRevB.107.115140

The recent observed anomalous Hall effect in magic angle twisted bilayer graphene (TBG) aligned to hexagonal boron nitride (hBN) and unconventional ferroelectricity in Bernal bilayer graphene sandwiched by hBN present a platform to tune the correlated properties in graphene systems. In these graphene-based moir?? superlattices, the aligned hBN substrate plays an important role. In this paper, we analyze the effects of hBN substrate on the band structure of the TBG. By means of an atomistic tight-binding model we calculate the electronic properties of TBG suspended and encapsulated with hBN. Interestingly, we found that the physical properties of TBG are extremely sensitive to the presence of hBN and they may be completely different if TBG is suspended or encapsulated. We quantify these differences by analyzing their electronic properties and band topology. We found that the narrow bandwidth, band gap, and local density of states are significantly modified by the aligned hBN substrates. Interestingly, these electronic properties can be used as a signature of the alignment in experiment. Moreover, the TBG/hBN superlattices in the presence or absence of the twofold rotation symmetry respond differently to the external electric field. For the TBG suspended in the hBN, application of an electric field results in the charge unevenly distributed between graphene layers, which can be used to tune the strength of the valley Hall effect or the anomalous Hall effect. Such rich topological phase diagram in these systems may be useful for experiments.

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