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Cited by 489

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All Magic Angles in Twisted Bilayer Graphene are Topological

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Song, Zhida, Wang, Zhijun, Shi, Wujun, Li, Gang, Fang, Chen, Bernevig, B. Andrei·2019·Physical Review Letters

Abstract

We show that the electronic structure of the low-energy bands in the small angle-twisted bilayer graphene consists of a series of semimetallic and topological phases. In particular, we are able to prove, using an approximate low-energy particle-hole symmetry, that the gapped set of bands that exist around all magic angles have a nontrivial topology stabilized by a magnetic symmetry, provided band gaps appear at fillings of ±4 electrons per moiré unit cell. The topological index is given as the winding number (a Z number) of the Wilson loop in the moiré Brillouin zone. Furthermore, we also claim that, when the gapped bands are allowed to couple with higher-energy bands, the Z index collapses to a stable Z_{2} index. The approximate, emergent particle-hole symmetry is essential to the topology of graphene: When strongly broken, nontopological phases can appear. Our Letter underpins topology as the crucial ingredient to the description of low-energy graphene. We provide a four-band short-range tight-binding model whose two lower bands have the same topology, symmetry, and flatness as those of the twisted bilayer graphene and which can be used as an effective low-energy model. We then perform large-scale (11000 atoms per unit cell, 40 days per k-point computing time) ab initio calculations of a series of small angles, from 3° to 1°, which show a more complex and somewhat different evolution of the symmetry of the low-energy bands than that of the theoretical moiré model but which confirm the topological nature of the system.

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Metadata

Authors
Song, Z., Wang, Z., Shi, W., Li, G., Fang, C., & Bernevig, B. A.
Venue
Physical Review Letters
Published
2019-07-16
Volume
123
Issue
3
Pages
036401-036401
ISSN
  • 0031-9007 (ISSN-L)
  • 1079-7114
OpenAlex
W2884381403
Cited by
489
References
50
FWCI
29.33
Type
journal article
Language
en
Open access
green

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CoChat. (2026). Citation check: All Magic Angles in Twisted Bilayer Graphene are Topological. https://app.cochat.ai/papers/10.1103/physrevlett.123.036401
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Song, Z., Wang, Z., Shi, W., Li, G., Fang, C., & Bernevig, B. A. (2019). All Magic Angles in Twisted Bilayer Graphene are Topological. Physical Review Letters. https://doi.org/10.1103/physrevlett.123.036401

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