paper

Strongly Interacting Phases in Twisted Bilayer Graphene at the Magic Angle

arXiv:2308.03843 · doi:10.1103/PhysRevB.110.L121123

Abstract

Twisted bilayer graphene near the magic angle is known to have a cascade of insulating phases at integer filling factors of the low-energy bands. In this Letter we address the nature of these phases through an unrestricted, large-scale Hartree-Fock calculation on the lattice that self-consistently accounts for all electronic bands. Using numerically unbiased methods, we show that Coulomb interactions produce ferromagnetic insulating states at integer fillings with maximal spin polarization . We find that the state is a pure ferromagnet, whereas all other insulating states are spin-valley polarized. At odd filling factors those states have a quantum anomalous Hall effect with Chern number . Except for the states, all other integer fillings have insulating phases with additional sublattice symmetry breaking and antiferromagnetism in the remote bands. We map the metal-insulator transitions of these phases as a function of the effective dielectric constant. Our results establish the importance of large-scale lattice calculations to faithfully determine the ground states of TBG at integer fillings.

5+1 pages, 3 figures

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