Intrinsic Layer Polarization and Multi-flatband Transport in Non-centrosymmetric Mixed-Stacked Multilayer Graphene

Graphene multilayers exhibit electronic spectra that depend sensitively on the layer number and stacking order. Here, we investigate ABCBC-stacked pentalayer graphene, a non-centrosymmetric mixed stacking that combines a rhombohedral trilayer-like cubic band and a Bernal bilayer-like parabolic band. Transport measurements reveal an intrinsic gap at charge neutrality that evolves strongly asymmetrically under a perpendicular displacement field, evidencing built-in layer polarization from broken inversion and mirror symmetry. By tuning the displacement field and carrier density, we drive multiple Lifshitz transitions and observe Landau levels with distinct degeneracies arising from the multi-flatband structure. Remarkably, a ν = -6 quantum Hall state emerges at an exceptionally low magnetic field of ∼20 mT. These results demonstrate that mixed-stacked multilayer graphene provides a tunable platform in which non-centrosymmetric symmetry breaking, multiple flatbands, and unusual quantum Hall physics coexist, opening opportunities to explore emergent correlated and topological electronic states.