An accurate tight binding model for twisted bilayer graphene describes topological flat bands without geometric relaxation
arxiv(2021)
摘要
A major hurdle in understanding the phase diagram of twisted bilayer graphene
(TBLG) are the roles of lattice relaxation and electronic structure on isolated
band flattening near magic twist angles. In this work, the authors develop an
accurate local environment tight binding model (LETB) fit to tight binding
parameters computed from ab initio density functional theory (DFT)
calculations across many atomic configurations. With the accurate
parameterization, it is found that the magic angle shifts to slightly lower
angles than often quoted, from around 1.05^∘ to around 0.99^∘, and
that isolated flat bands appear for rigidly rotated graphene layers, with
enhancement of the flat bands when the layers are allowed to distort. Study of
the orbital localization supports the emergence of fragile topology in the
isolated flat bands without the need for lattice relaxation.
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