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; Xiaomu Wang

doi:10.1038/s41586-022-04520-8

Observation of chiral and slow plasmons in twisted bilayer graphene

Nature. 2022 May;605(7908):63-68. doi: 10.1038/s41586-022-04520-8. Epub 2022 May 4.

Authors

Tianye Huang^#¹, Xuecou Tu^#¹, Changqing Shen², Binjie Zheng¹, Junzhuan Wang¹, Hao Wang³, Kaveh Khaliji⁴, Sang Hyun Park⁴, Zhiyong Liu⁵, Teng Yang⁵, Zhidong Zhang⁵, Lei Shao³, Xuesong Li^{6

7}, Tony Low^{8

9}, Yi Shi¹⁰, Xiaomu Wang¹¹

Affiliations

¹ School of Electronic Science and Engineering, Nanjing University, Nanjing, China.
² School of electronic science and engineering, University of Electronic Science and Technology of China, Chengdu, China.
³ Beijing Computational Science Research Centre, Beijing, China.
⁴ Department of Electrical & Computer Engineering, University of Minnesota, Minneapolis, MN, USA.
⁵ Shenyang National Laboratory for Materials Science, Institute of Metal Research, Chinese Academy of Sciences, Shenyang, China.
⁶ School of electronic science and engineering, University of Electronic Science and Technology of China, Chengdu, China. lxs@uestc.edu.cn.
⁷ Shenzhen Institute for Advanced Study, University of Electronic Science and Technology of China, Shenzhen, China. lxs@uestc.edu.cn.
⁸ Department of Electrical & Computer Engineering, University of Minnesota, Minneapolis, MN, USA. tlow@umn.edu.
⁹ Department of Physics, University of Minnesota, Minneapolis, MN, USA. tlow@umn.edu.
¹⁰ School of Electronic Science and Engineering, Nanjing University, Nanjing, China. yshi@nju.edu.cn.
¹¹ School of Electronic Science and Engineering, Nanjing University, Nanjing, China. xiaomu.wang@nju.edu.cn.

^# Contributed equally.

PMID: 35508778
DOI: 10.1038/s41586-022-04520-8

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 techniques^3-7, 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.

Publication types

Research Support, Non-U.S. Gov't