Heavy Fermion Insights into the Normal State of MATBG

Experiments have revealed a paradox in magic-angle twisted bilayer graphene (MATBG) above symmetry breaking temperatures. Scanning tunneling microscopy and entropy measurements provide evidence for Mott physics and local moments, yet single electron transistor measurements reveal 'Dirac revivals' — itinerant character reemerging near integer fillings. While momentum space continuum models have been valuable, capturing localized physics remains challenging. The topological heavy fermion (THF) model addresses this by describing the flat bands as exponentially localized Wannier orbitals hybridized with a relativistic conduction sea, naturally incorporating interactions, topology, and all symmetries within a mixed real and momentum space model. Synthesizing heavy fermion physics and MATBG experiments, we introduce a phenomenological THF model with only onsite interactions and an emergent binding potential to simultaneously capture Mott physics and Dirac revivals, interpreting the latter as electrons sloshing between the topological sea and localized states. We [1] identify a key discrepancy between measured and calculated onsite Coulomb interactions, implicating renormalization beyond current treatments. Two features distinguish MATBG from conventional rare-earth materials: the relativistic topological sea produces two energy scales, a high temperature scale for hybridization onset between the local moments and relativistic electrons that establishes topology, and a low temperature scale for flat band coherence in a heavy Fermi liquid. Second, optical phonons are fast compared to electron valence fluctuations. We demonstrate [2] in a toy model that fast phonons can renormalize onsite interactions, potentially reconciling ab initio and experimental discrepancies while introducing important effective electron-electron interactions. Finally, we extract key experimental features of the persistent filling independent excitation observed in recent quantum twist microscopy, establishing crucial constraints for future theoretical developments.