In-plane Chiral Tunneling and Out-of-plane Valley-polarized Quantum Tunneling in Twisted Graphene Trilayer

Here we show that twisted graphene trilayer made by misoriented stacking a graphene monolayer on top of a Bernal graphene bilayer can exhibit rich and tailored electronic properties. For the case that the graphene monolayer and bilayer are strongly coupled, both the massless Dirac fermions and massive chiral fermions coexist in the twisted trilayer, leading to unique in-plane chiral tunneling. For a weak coupling between the two graphene systems, the distinct chiralities and pseudospin textures of quasiparticles in monolayer and bilayer enable vertical valley-polarized quantum tunneling between them. Intriguingly, the polarity of the valley polarization can be inverted by controlling the rotational angles between the two systems. Our results indicate that layered van der Waals structures assembled from individual atomic planes can create materials that harbor unusual properties and new functionalities depending on how the crystalline layers are stacked.