Observation of chiral and slow plasmons in twisted bilayer graphene

Tianye Huang, Xuecou Tu, Changqing Shen, Binjie Zheng, Junzhuan Wang, Hao Wang, Kaveh Khaliji, Sang Hyun Park, Zhiyong Liu, Teng Yang, Zhidong Zhang, Lei Shao, Xuesong Li (), Tony Low (), Yi Shi () and Xiaomu Wang ()
Additional contact information
Tianye Huang: Nanjing University
Xuecou Tu: Nanjing University
Changqing Shen: University of Electronic Science and Technology of China
Binjie Zheng: Nanjing University
Junzhuan Wang: Nanjing University
Hao Wang: Beijing Computational Science Research Centre
Kaveh Khaliji: University of Minnesota
Sang Hyun Park: University of Minnesota
Zhiyong Liu: Institute of Metal Research, Chinese Academy of Sciences
Teng Yang: Institute of Metal Research, Chinese Academy of Sciences
Zhidong Zhang: Institute of Metal Research, Chinese Academy of Sciences
Lei Shao: Beijing Computational Science Research Centre
Xuesong Li: University of Electronic Science and Technology of China
Tony Low: University of Minnesota
Yi Shi: Nanjing University
Xiaomu Wang: Nanjing University

Nature, 2022, vol. 605, issue 7908, 63-68

Abstract: Abstract Moiré superlattices have led to observations of exotic emergent electronic properties such as superconductivity and strong correlated states in small-rotation-angle twisted bilayer graphene (tBLG)1,2. Recently, these findings have inspired the search for new properties in moiré plasmons. Although plasmon propagation in the tBLG basal plane has been studied by near-field nano-imaging techniques3–7, the general electromagnetic character and properties of these plasmons remain elusive. Here we report the direct observation of two new plasmon modes in macroscopic tBLG with a highly ordered moiré superlattice. Using spiral structured nanoribbons of tBLG, we identify signatures of chiral plasmons that arise owing to the uncompensated Berry flux of the electron gas under optical pumping. The salient features of these chiral plasmons are shown through their dependence on optical pumping intensity and electron fillings, in conjunction with distinct resonance splitting and Faraday rotation coinciding with the spectral window of maximal Berry flux. Moreover, we also identify a slow plasmonic mode around 0.4 electronvolts, which stems from the interband transitions between the nested subbands in lattice-relaxed AB-stacked domains. This mode may open up opportunities for strong light–matter interactions within the highly sought after mid-wave infrared spectral window8. Our results unveil the new electromagnetic dynamics of small-angle tBLG and exemplify it as a unique quantum optical platform.

Date: 2022
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DOI: 10.1038/s41586-022-04520-8

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