Magic-angle twisted bilayer graphene as a topological heavy fermion problem

ZD Song, BA Bernevig - Physical review letters, 2022 - APS
Magic-angle (θ= 1.0 5°) twisted bilayer graphene (MATBG) has shown two seemingly
contradictory characters: the localization and quantum-dot-like behavior in STM …

Twisted bilayer graphene. IV. Exact insulator ground states and phase diagram

B Lian, ZD Song, N Regnault, DK Efetov, A Yazdani… - Physical Review B, 2021 - APS
We derive the exact insulator ground states of the projected Hamiltonian of magic-angle
twisted bilayer graphene (TBG) flat bands with Coulomb interactions in various limits, and …

Twisted bilayer graphene. III. Interacting Hamiltonian and exact symmetries

BA Bernevig, ZD Song, N Regnault, B Lian - Physical Review B, 2021 - APS
We derive the explicit Hamiltonian of twisted bilayer graphene (TBG) with Coulomb
interaction projected into the flat bands and study the symmetries of the Hamiltonian. First …

Kondo lattice model of magic-angle twisted-bilayer graphene: Hund's rule, local-moment fluctuations, and low-energy effective theory

H Hu, BA Bernevig, AM Tsvelik - Physical review letters, 2023 - APS
We apply a generalized Schrieffer-Wolff transformation to the extended Anderson-like
topological heavy fermion (THF) model for the magic-angle (θ= 1.0 5°) twisted bilayer …

Twisted bilayer graphene. V. Exact analytic many-body excitations in Coulomb Hamiltonians: Charge gap, Goldstone modes, and absence of Cooper pairing

BA Bernevig, B Lian, A Cowsik, F Xie, N Regnault… - Physical Review B, 2021 - APS
We find exact analytic expressions for the energies and wave functions of the charged and
neutral excitations above the exact ground states (at rational filling per unit cell) of projected …

Twisted bilayer graphene. VI. An exact diagonalization study at nonzero integer filling

F Xie, A Cowsik, ZD Song, B Lian, BA Bernevig… - Physical Review B, 2021 - APS
Using exact diagonalization, we study the projected Hamiltonian with the Coulomb
interaction in the eight flat bands of first magic angle twisted bilayer graphene. Employing …

Twisted bilayer graphene. II. Stable symmetry anomaly

ZD Song, B Lian, N Regnault, BA Bernevig - Physical Review B, 2021 - APS
We show that the entire continuous model of twisted bilayer graphene (TBG)(and not just the
two active bands) with particle-hole symmetry is anomalous and hence incompatible with …

Twisted bilayer graphene. I. Matrix elements, approximations, perturbation theory, and a two-band model

BA Bernevig, ZD Song, N Regnault, B Lian - Physical Review B, 2021 - APS
We investigate the twisted bilayer graphene (TBG) model of Bistritzer and MacDonald
(BM)[Bistritzer and MacDonald, Proc. Natl. Acad. Sci. 108, 12233 (2011) PNASA6 0027 …

Symmetric kondo lattice states in doped strained twisted bilayer graphene

H Hu, G Rai, L Crippa, J Herzog-Arbeitman… - Physical review …, 2023 - APS
We use the topological heavy fermion (THF) model and its Kondo lattice (KL) formulation to
study the possibility of a symmetric Kondo (SK) state in twisted bilayer graphene. Via a large …

Dynamical correlations and order in magic-angle twisted bilayer graphene

G Rai, L Crippa, D Călugăru, H Hu, F Paoletti… - Physical Review X, 2024 - APS
The interplay of dynamical correlations and electronic ordering is pivotal in shaping phase
diagrams of correlated quantum materials. In magic-angle twisted bilayer graphene …