The single-particle and many-body properties of twisted bilayer graphene (TBG) can be dramatically different from those of a single graphene layer, particularly when the two layers are rotated relative to each other by a small angle (θ ≈ 1°), owing to the moiré potential induced by the twist. Here we probe the collective excitations of TBG with a spatial resolution of 20 nm, by applying mid-infrared near-field optical microscopy. We find a propagating plasmon mode in charge-neutral TBG for θ = 1.1−1.7°, which is different from the intraband plasmon in single-layer graphene. We interpret it as an interband plasmon associated with the optical transitions between minibands originating from the moiré superlattice. The details of the plasmon dispersion are directly related to the motion of electrons in the moiré superlattice and offer an insight into the physical properties of TBG, such as band nesting between the flat band and remote band, local interlayer coupling, and losses. We find a strongly reduced interlayer coupling in the regions with AA stacking, pointing at screening due to electron–electron interactions. Optical nano-imaging of TBG allows the spatial probing of interaction effects at the nanoscale and potentially elucidates the contribution of collective excitations to many-body ground states.

扭曲双层石墨烯 (TBG) 的单粒子和多体特性可能与单层石墨烯的特性有很大不同，特别是当两层相对于彼此旋转小角度 ( θ≈1  °) 时，由于扭曲引起的莫尔电位。在这里，我们通过应用中红外近场光学显微镜以 20 nm 的空间分辨率探测 TBG 的集体激发。我们在电荷中性 TBG 中找到了传播等离子体模式，用于θ = 1.1-1.7°，这与单层石墨烯中的带内等离子体不同。我们将其解释为与源自莫尔超晶格的小波段之间的光学跃迁相关的带间等离子体。等离激元色散的细节与莫尔超晶格中电子的运动直接相关，并提供了对 TBG 物理特性的深入了解，例如平带和远程带之间的带嵌套、局部层间耦合和损耗。我们发现在具有 AA 堆叠的区域中层间耦合强烈降低，指向由于电子 - 电子相互作用而导致的屏蔽。TBG 的光学纳米成像允许在纳米尺度上对相互作用效应进行空间探测，并可能阐明集体激发对多体基态的贡献。