Coexisting Massive and Massless Dirac Fermions in Moire'-Reconstructed Bilayer Graphene

Abstract

We report the emergence of massless Dirac fermions in moir\'{e}-reconstructed bands of bilayer graphene (BLG) aligned with hexagonal boron nitride (hBN). Magnetotransport measurements reveal that while the primary BLG band retains a parabolic dispersion with a Berry phase of $2\pi$, the moir\'{e}-induced secondary bands at $n/n_0 = \pm 4$ host chiral massless quasiparticles with a Berry phase $\pi$ and a Fermi velocity $v_m \approx 3.6 \times 10^5 \mathrm{m s^{-1}}$. This transition from massive to massless carriers arises from topological band reconstruction driven by the hBN moir\'{e} potential. Our results demonstrate that moir\'{e} engineering in BLG/hBN offers a powerful route to tune band topology and realize coexisting Dirac and massive fermions within a single crystalline platform.