Observation of interband collective excitations in twisted bilayer graphene
Observation of interband collective excitations in twisted bilayer graphene
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DOI：
10.1038/s41567-021-01327-8
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发表时间：
2021-09-27
期刊：
影响因子：
19.6
通讯作者：
Koppens, Frank H. L.
中科院分区：
文献类型：
--
作者：
Hesp, Niels C. H.;Torre, Iacopo;Koppens, Frank H. L.
莫尔势极大地改变了神奇扭曲角扭曲双层石墨烯的电子特性。可以通过光学纳米成像观察到的传播等离激元模式与莫尔微带之间的跃迁相关。扭曲双层石墨烯 (TBG) 的单粒子和多体特性可能与单石墨烯层的单粒子和多体特性显着不同，特别是当两层相对于彼此旋转小角度（θ 大约为 1 度）时，由于扭曲引起的莫尔势。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 中发现了 θ = 1.1-1.7 度的传播等离子体激元模式，这与单层石墨烯中的带内等离子体激元不同。我们将其解释为与源自莫尔超晶格的微带之间的光学跃迁相关的带间等离子体激元。等离子体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 AA 堆叠区域的层间耦合大大减少，这表明由于电子-电子相互作用而产生了屏蔽。 TBG 的光学纳米成像允许在纳米尺度上空间探测相互作用效应，并有可能阐明集体激发对多体基态的贡献。
Moire potentials substantially alter the electronic properties of twisted bilayer graphene at a magic twist angle. A propagating plasmon mode, which can be observed with optical nano-imaging, is associated with transitions between the moire minibands.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 (theta approximate to 1 degrees), owing to the moire 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 theta = 1.1-1.7 degrees, 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 moire superlattice. The details of the plasmon dispersion are directly related to the motion of electrons in the moire 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.