Kondo Lattice Model of Magic-Angle Twisted-Bilayer Graphene: Hund’s Rule, Local-Moment Fluctuations, and Low-Energy Effective Theory
For this work, we apply a generalized Schrieffer-Wolff transformation to the extended Anderson-like topological heavy fermion (THF) model for the magic-angle (θ=1.05°) twisted bilayer graphene (MATBLG) [Phys. Rev. Lett. 129, 047601 (2022)], to obtain its Kondo lattice limit. In this limit localized $$\mathcal{f}$$ electrons on a triangular lattice interact with topological conduction $$\mathcal{c}$$ electrons. By solving the exact limit of the THF model, we show that the integer fillings ν=0, ±1, ±2 are controlled by the heavy $$\mathcal{f}$$ electrons, while ν=±3 is at the border of a phase transition between two $$\mathcal{f}$$-electron fillings. For ν=0, ±1, ±2, we then calculatemore »