Magic-angle twisted symmetric trilayer graphene as a topological heavy-fermion problem

A topological heavy-fermion (THF) model is formulated for magical-angle twisted symmetric trilayer graphene (MATSTG), where ``symmetric'' means that the top and bottom layers are rotated equally with respect to the middle layer. In addition to the localized f modes and itinerant c modes (which serve as the basis of the THF model for twisted bilayer graphene), the THF model of MATSTG consists of extra Dirac (d) modes. The newly proposed f-c-d THF model can well reproduce previous numerical results on the correlated phases at integer fillings, and can provide a new analytical understanding of them at charge neutrality.