Continuum models for twisted bilayer graphene: Effect of lattice deformation and hopping parameters

F Guinea and NR Walet, PHYSICAL REVIEW B, 99, 205134 (2019).

DOI: 10.1103/PhysRevB.99.205134

We analyze a description of twisted graphene bilayers that incorporates the deformation of the layers using state-of-the-art interlayer atomic potentials and a modification of the hopping parameters between layers in the light of the classic Slonczewski-Weiss-McClure parametrization. We obtain narrow bands in all cases, but their nature can be rather different. We will show how to describe the results by equivalent continuum models. Even though such models can be constructed, their complexity can vary, requiring many coupling parameters to be included, and the full in-layer dispersion must be taken into account. The combination of all these effects will have a large impact on the wave functions of the flat bands, and modifications in details of the underlying models can lead to significant changes. A robust conclusion is that the natural strength of the interlayer couplings is higher than usually assumed, leading to shifts in the definition of the magic angles. The structure at the edges of the narrow bands, at the Gamma point of the Brillouin zone is also strongly dependent on parametrization. As a result, the existence, and size, of band gaps between the flat bands and the neighboring ones are changed. Hence, the definition of Wannier functions, and descriptions based on local interactions are strongly dependent on the description of the model at the atomic scale.

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