Understanding and tuning correlated states is of great interest and importance to modern condensed-matter physics. The recent discovery of unconventional superconductivity and Mott-like insulating states in magic-angle twisted bilayer graphene presents a unique platform to study correlation phenomena, in which the Coulomb energy dominates over the quenched kinetic energy as a result of hybridized flat bands. Extending this approach to the case of twisted multilayer graphene would allow even higher control over the band structure because of the reduced symmetry of the system. Here we study electronic transport properties of twisted monolayer–bilayer graphene (a bilayer on top of monolayer graphene heterostructure). We observe the formation of van Hove singularities that are highly tunable by changing either the twist angle or external electric field and can cause strong correlation effects under optimum conditions. We provide basic theoretical interpretations of the observed electronic structure.

理解和调整相关态对现代凝聚态物理学具有极大的兴趣和重要性。最近在魔角扭曲双层石墨烯中发现的非常规超导性和类莫特绝缘状态为研究相关现象提供了一个独特的平台，其中库仑能量由于杂化平带而优于淬火动能。由于系统的对称性降低，将这种方法扩展到扭曲多层石墨烯的情况将允许对能带结构进行更高的控制。在这里，我们研究了扭曲的单层 - 双层石墨烯（单层石墨烯异质结构顶部的双层）的电子传输特性。我们观察到范霍夫奇点的形成，这些奇点可以通过改变扭转角或外部电场进行高度可调，并且在最佳条件下会产生强相关效应。我们提供了观察到的电子结构的基本理论解释。