A self-consistent Hartree theory for lattice-relaxed magic-angle twisted bilayer graphene

We usually think of magic-angle twisted bilayer graphene in terms of the non-interacting Bistritzer-MacDonald (BM) flat bands. In this talk, I will present our recent results showing the emergence of an ultraflat band (~8 meV) when both lattice relaxation [1] and the Hartree interaction [2] are considered. These bands differ significantly from the BM bands, including in their robustness to changing carrier density. This stability is partly due to a Lifshitz transition to a Fermi surface topology that supports a "heavy fermion" pocket at the Gamma point that stabilizes the flat band. This phenomenon occurs within a narrow "magic angle range" that coincides with experimental observations of superconductivity. Finally, I will discuss why the expected Fock contributions are much weaker in experiment. References: [1] Analytical Model for Atomic Relaxation in Twisted Moiré Materials, MM Al Ezzi, GN Pallewela, C De Beule, EJ Mele, and S Adam, arXiv:2401.00498 (2024). [2] A self-consistent Hartree theory for lattice-relaxed magic-angle twisted bilayer graphene, MM Al Ezzi, L. Peng, Z. Liu, JHZ Chao, GN Pallewela, D. Foo, and S Adam, arXiv:2404.17638 (2024).