Isolated Flat Bands in Small-Angle Twisted Bilayer Graphene via hBN Alignment

Twisted bilayer graphene (TBG) at the magic angle (~1.05°) has attracted extensive attention due to correlated and topological phenomena associated with its flat bands. While TBG also hosts flat bands at smaller twist angles, these bands are typically not isolated and have received less attention. We show that aligning a hexagonal boron nitride (hBN) layer with TBG induces isolated flat bands in the small-angle regime. Using Hartree-Fock calculations, we further discuss the emergence of correlated electronic phases in these flat bands, highlighting the role of substrate engineering in realizing novel correlated states beyond the magic-angle regime.