Degenerate Flat Bands in Twisted Bilayer Graphene.

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Title: Degenerate Flat Bands in Twisted Bilayer Graphene.
Authors: Becker, Simon1 (AUTHOR) simon.becker@math.ethz.ch, Humbert, Tristan2 (AUTHOR) tristan.humbert@ens.psl.eu, Zworski, Maciej2 (AUTHOR) zworski@math.berkeley.edu
Source: Archive for Rational Mechanics & Analysis. Feb2026, Vol. 250 Issue 1, p1-45. 45p.
Subjects: Graphene, Hamiltonian mechanics, Multiplicity (Mathematics), Quantum mechanics, Geometric quantum phases, Bloch's theorem
Abstract: We prove that in the chiral limit of the Bistritzer–MacDonald Hamiltonian, there exist magic angles at which the Hamiltonian exhibits flat bands of multiplicity four instead of two. We analyse the structure of Bloch functions associated with the bands of arbitrary multiplicity, compute the corresponding Chern number to be - 1 , and show that there exist infinitely many degenerate magic angles for a generic choice of tunnelling potential, including the Bistritzer–MacDonald potential. Moreover, we demonstrate for generic tunnelling potentials that flat bands have only twofold or fourfold multiplicities. [ABSTRACT FROM AUTHOR]
Copyright of Archive for Rational Mechanics & Analysis is the property of Springer Nature and its content may not be copied or emailed to multiple sites without the copyright holder's express written permission. Additionally, content may not be used with any artificial intelligence tools or machine learning technologies. However, users may print, download, or email articles for individual use. This abstract may be abridged. No warranty is given about the accuracy of the copy. Users should refer to the original published version of the material for the full abstract. (Copyright applies to all Abstracts.)
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  Data: <searchLink fieldCode="JN" term="%22Archive+for+Rational+Mechanics+%26+Analysis%22">Archive for Rational Mechanics & Analysis</searchLink>. Feb2026, Vol. 250 Issue 1, p1-45. 45p.
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  Data: <searchLink fieldCode="DE" term="%22Graphene%22">Graphene</searchLink><br /><searchLink fieldCode="DE" term="%22Hamiltonian+mechanics%22">Hamiltonian mechanics</searchLink><br /><searchLink fieldCode="DE" term="%22Multiplicity+%28Mathematics%29%22">Multiplicity (Mathematics)</searchLink><br /><searchLink fieldCode="DE" term="%22Quantum+mechanics%22">Quantum mechanics</searchLink><br /><searchLink fieldCode="DE" term="%22Geometric+quantum+phases%22">Geometric quantum phases</searchLink><br /><searchLink fieldCode="DE" term="%22Bloch's+theorem%22">Bloch's theorem</searchLink>
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  Data: We prove that in the chiral limit of the Bistritzer–MacDonald Hamiltonian, there exist magic angles at which the Hamiltonian exhibits flat bands of multiplicity four instead of two. We analyse the structure of Bloch functions associated with the bands of arbitrary multiplicity, compute the corresponding Chern number to be - 1 , and show that there exist infinitely many degenerate magic angles for a generic choice of tunnelling potential, including the Bistritzer–MacDonald potential. Moreover, we demonstrate for generic tunnelling potentials that flat bands have only twofold or fourfold multiplicities. [ABSTRACT FROM AUTHOR]
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  Data: <i>Copyright of Archive for Rational Mechanics & Analysis is the property of Springer Nature and its content may not be copied or emailed to multiple sites without the copyright holder's express written permission. Additionally, content may not be used with any artificial intelligence tools or machine learning technologies. However, users may print, download, or email articles for individual use. This abstract may be abridged. No warranty is given about the accuracy of the copy. Users should refer to the original published version of the material for the full abstract.</i> (Copyright applies to all Abstracts.)
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        Value: 10.1007/s00205-025-02155-3
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      – SubjectFull: Multiplicity (Mathematics)
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      – SubjectFull: Geometric quantum phases
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      – SubjectFull: Bloch's theorem
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      – TitleFull: Degenerate Flat Bands in Twisted Bilayer Graphene.
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              Text: Feb2026
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