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Faithful tight-binding models and fragile topology of magic-angle bilayer graphene

Journal Article · · Physical Review. B
 [1];  [2];  [3];  [4]
  1. Harvard Univ., Cambridge, MA (United States); Massachusetts Inst. of Technology (MIT), Cambridge, MA (United States); DOE/OSTI
  2. Harvard Univ., Cambridge, MA (United States); Massachusetts Inst. of Technology (MIT), Cambridge, MA (United States)
  3. Massachusetts Inst. of Technology (MIT), Cambridge, MA (United States)
  4. Harvard Univ., Cambridge, MA (United States)

Correlated insulators and superconductivity have been observed in “magic-angle” twisted bilayer graphene, when the nearly flat bands close to neutrality are partially filled. Here, 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.

Research Organization:
Massachusetts Inst. of Technology (MIT), Cambridge, MA (United States)
Sponsoring Organization:
USDOE Office of Science (SC)
Grant/Contract Number:
SC0008739
OSTI ID:
1611147
Alternate ID(s):
OSTI ID: 1523316
Journal Information:
Physical Review. B, Journal Name: Physical Review. B Journal Issue: 19 Vol. 99; ISSN 2469-9950
Publisher:
American Physical Society (APS)Copyright Statement
Country of Publication:
United States
Language:
English

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Electronic correlations in twisted bilayer graphene near the magic angle journal August 2019
Superconductors, orbital magnets and correlated states in magic-angle bilayer graphene journal October 2019
Stiefel–Whitney classes and topological phases in band theory journal October 2019
Flatbands and Perfect Metal in Trilayer Moiré Graphene journal July 2019
Cold atoms in twisted-bilayer optical potentials journal November 2019
Ferromagnetism and spin-valley liquid states in moiré correlated insulators journal July 2019
Designing flat bands by strain journal July 2019
Classification of crystalline insulators without symmetry indicators: Atomic and fragile topological phases in twofold rotation symmetric systems journal September 2019
Twist-angle sensitivity of electron correlations in moiré graphene bilayers journal September 2019
Twist, slip, and circular dichroism in bilayer graphene journal September 2019
Internal screening and dielectric engineering in magic-angle twisted bilayer graphene journal October 2019
Fragile topology protected by inversion symmetry: Diagnosis, bulk-boundary correspondence, and Wilson loop journal November 2019
Attractive electron-electron interactions from internal screening in magic-angle twisted bilayer graphene journal December 2019
Pairing and non-Fermi liquid behavior in partially flat-band systems: Beyond nesting physics journal January 2020
Superfluid weight and Berezinskii-Kosterlitz-Thouless transition temperature of twisted bilayer graphene journal February 2020
All Magic Angles in Twisted Bilayer Graphene are Topological journal July 2019
Valence Bond Orders at Charge Neutrality in a Possible Two-Orbital Extended Hubbard Model for Twisted Bilayer Graphene journal October 2019
Geometric and Conventional Contribution to the Superfluid Weight in Twisted Bilayer Graphene journal December 2019
Nature of the Correlated Insulator States in Twisted Bilayer Graphene journal March 2020
Exact continuum model for low-energy electronic states of twisted bilayer graphene journal August 2019
Derivation of Wannier orbitals and minimal-basis tight-binding Hamiltonians for twisted bilayer graphene: First-principles approach journal November 2019
Twisted bilayer graphene aligned with hexagonal boron nitride: Anomalous Hall effect and a lattice model journal November 2019
Fragile topologically protected perfect reflection for acoustic waves journal February 2020
Quantum Valley Hall Effect, Orbital Magnetism, and Anomalous Hall Effect in Twisted Multilayer Graphene Systems journal August 2019
Valley Jahn-Teller Effect in Twisted Bilayer Graphene journal October 2019
Correlated insulating and superconducting states in twisted bilayer graphene below the magic angle journal September 2019
Electronic correlations in twisted bilayer graphene near the magic angle text January 2019
Imaging Electronic Correlations in Twisted Bilayer Graphene near the Magic Angle text January 2019
An exact continuum model for low-energy electronic states of twisted bilayer graphene text January 2019
Designing Flat Band by Strain text January 2019
Quantum valley Hall effect, orbital magnetism, and anomalous Hall effect in twisted multilayer graphene systems text January 2019
Stiefel-Whitney classes and topological phases in band theory text January 2019
Valley Jahn-Teller effect in twisted bilayer graphene text January 2019
Geometric and conventional contribution to superfluid weight in twisted bilayer graphene text January 2019
Classification of crystalline insulators without symmetry indicators: atomic and fragile topological phases in twofold rotation symmetric systems text January 2019