Local Kekulé distortion turns twisted bilayer graphene into topological Mott insulators and superconductors

Abstract

Magic-angle twisted bilayer graphene displays at different fillings of the four flat bands lying around the charge neutrality point a wealth of notable phases that include magnetic Chern insulators, whose magnetization is mostly of orbital nature, and contiguous superconducting domes. Such rich phase diagram is here explained through the positive interplay of Coulomb repulsion and the electron coupling to a twofold optical mode that corresponds to Kekulè distortions localized into the small AA stacked regions of the moiré supercells. A static distortion stabilizes, at any integer filling of the flat bands, valence-bond insulators that carry finite Chern number away from charge neutrality. Similarly, a dynamic distortion that resonates between the two lattice vibrations leads to resonating-valence-bond topological insulators with built-in chiral d-wave pairs that have finite Chern number equal to the angular momentum, and thus are prone to turn superconducting upon doping away from integer filling.

7 pages plus references, 5 figures. Supplementary Material can be requested at [email protected]

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Cited by in corpus (21)

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• Truncated atomic plane wave method for the subband structure calculations of Moiré systems
• Molecular Pairing in Twisted Bilayer Graphene Superconductivity
• Electron-phonon coupling and competing Kekulé orders in twisted bilayer graphene
• Flat-band optical phonons in twisted bilayer graphene
• Theory of Topological Superconductivity and Antiferromagnetic Correlated Insulators in Twisted Bilayer WSe${}_2$
• Electron phonon coupling in the topological heavy fermion model of twisted bilayer graphene
• Moiré optical phonons dancing with heavy electrons in magic-angle twisted bilayer graphene
• Resonating Valence Bond States in an Electron-Phonon System
• Kekulé spirals and charge transfer cascades in twisted symmetric trilayer graphene
• Bending Stiffness Collapse, Buckling, Topological Bands of Freestanding Twisted Bilayer Graphene
• Textured Exciton Insulators
• Competing Correlated Insulators in multi-orbital systems coupled to phonons
• Kekulé valence bond order in the honeycomb lattice optical Su-Schrieffer-Heeger Model and its relevance to Graphene
• Coulomb-driven band unflattening suppresses $K$-phonon pairing in moiré graphene
• Band structure and optical response of Kekulé-modulated $\alpha -{\mathcal{T}}_3$ model
• Nonflat bands and chiral symmetry in magic-angle twisted bilayer graphene
• Correlation effects in magic-angle twisted bilayer graphene: An auxiliary-field quantum Monte Carlo study
• Mean-field Modelling of Moiré Materials: A User's Guide with Selected Applications to Twisted Bilayer Graphene