Degenerate Flat Bands in Twisted Bilayer Graphene.

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Bibliographic Details
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]
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Database: Engineering Source
Description
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]
ISSN:00039527
DOI:10.1007/s00205-025-02155-3