Faithful tight-binding models and fragile topology of magic-angle bilayer graphene
Name
PhysRevB.99.195455.pdf
Description
Published version
Size
2.14 MB
Format
Adobe PDF
Checksum (MD5)
4201a3c91daf22c62fa79b5dc9dffe98
Author(s)
Po, Hoi Chun
Zou, Liujun
Senthil, T
Vishwanath, Ashvin
Date Issued
2019
Journal
Physical Review B
Publisher
American Physical Society (APS)
Version
Final published version
Abstract
Correlated insulators and superconductivity have been observed in "magic-angle" twisted bilayer graphene, when the nearly flat bands close to neutrality are partially filled. While a momentum-space continuum model accurately describes these flat bands, interaction effects are more conveniently incorporated in tight-binding models. We have previously shown that no fully symmetric tight-binding model can be minimal, in the sense of capturing just the flat bands, so extended models are unavoidable. Here, we introduce a family of tight-binding models that capture the flat bands while simultaneously retaining all symmetries. In particular, we construct three concrete models with five, six, or ten bands per valley and per spin. These models are also faithful, in that the additional degrees of freedom represent energy bands further away from neutrality, and they serve as optimal starting points for a controlled study of interaction effects. Furthermore, our construction demonstrates the "fragile topology" of the nearly flat bands; i.e., the obstruction to constructing exponentially localized Wannier functions can be resolved when a particular set of trivial bands is added to the model.
MIT Department
Massachusetts Institute of Technology. Department of Physics
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DOI of Published Version
https://doi.org/10.1103/PHYSREVB.99.195455
