Many-body ground states from decomposition of ideal higher Chern bands: Applications to chirally twisted graphene multilayers

Motivated by the higher Chern bands of twisted graphene multilayers, we consider flat bands with arbitrary Chern number C with ideal quantum geometry. While C > 1 bands differ from Landau levels, we show that these bands host exact fractional Chern insulator (FCI) ground states for short-range interactions. We show how to decompose ideal higher Chern bands into separate ideal bands with Chern number 1 that are intertwined through translation and rotation symmetry. The decomposed bands admit an SU(C) action that combines real space and momentum space translations. Remarkably, they also allow for analytic construction of exact many-body ground states, such as generalized quantum Hall ferromagnets and FCIs, including flavor-singlet Halperin states and Laughlin ferromagnets in the limit of short-range interactions. In this limit, the SU(C) action is promoted to a symmetry on the ground-state subspace. While flavor singlet states are translation symmetric, the flavor ferromagnets correspond to translation broken states and admit charged skyrmion excitations corresponding to a spatially varying density wave pattern. We confirm our analytic predictions with numerical simulations of ideal bands of twisted chiral multilayers of graphene, and discuss consequences for experimentally accessible systems such as monolayer graphene twisted relative to a Bernal bilayer.

Automated summary

Motivated by higher Chern bands in twisted graphene multilayers, we investigate flat bands with arbitrary Chern number C and ideal quantum geometry. We find exact fractional Chern insulator (FCI) ground states for C > 1 bands with short-range interactions. By decomposing the higher Chern bands into separate bands with Chern number 1, we establish an SU(C) action combining real and momentum space translations and derive analytical constructions of FCI ground states. We confirm our predictions through numerical simulations and discuss implications for experimentally accessible systems such as monolayer graphene twisted relative to a Bernal bilayer.