Strong Moiré Excitons in High-Angle Twisted Transition Metal Dichalcogenide Homobilayers with Robust Commensuration

Xiaoxu Zhao; Jingsi Qiao; Xin Zhou; Hao Chen; Jun You Tan; Hongyi Yu; Si Min Chan; Jing Li; Henshui Zhang; Jiadong Zhou; Jiadong Dan; Zhen Liu; Wu Zhou; Zheng Liu; Bo Peng; Longjiang Deng; Stephen John Pennycook; Su Ying Quek; Kian Ping Loh

doi:10.1021/acs.nanolett.1c03622

Strong Moiré Excitons in High-Angle Twisted Transition Metal Dichalcogenide Homobilayers with Robust Commensuration

Nano Lett. 2022 Jan 12;22(1):203-210. doi: 10.1021/acs.nanolett.1c03622. Epub 2021 Dec 20.

Authors

Xiaoxu Zhao^{1

2}, Jingsi Qiao³, Xin Zhou⁴, Hao Chen⁴, Jun You Tan³, Hongyi Yu⁵, Si Min Chan¹, Jing Li^{3

4}, Henshui Zhang⁶, Jiadong Zhou², Jiadong Dan¹, Zhen Liu⁷, Wu Zhou⁸, Zheng Liu², Bo Peng⁷, Longjiang Deng⁷, Stephen John Pennycook⁸, Su Ying Quek^{1

3

9}, Kian Ping Loh^{3

4}

Affiliations

¹ Department of Materials Science and Engineering, National University of Singapore, 9 Engineering Drive 1, Singapore 117575, Singapore.
² School of Materials Science and Engineering, Nanyang Technological University, Singapore 639798, Singapore.
³ Centre for Advanced 2D Materials, National University of Singapore, 6 Science Drive 2, Singapore 117546, Singapore.
⁴ Department of Chemistry, National University of Singapore, 3 Science Drive 3, Singapore 117543, Singapore.
⁵ Guangdong Provincial Key Laboratory of Quantum Metrology and Sensing & School of Physics and Astronomy, Sun Yat-Sen University (Zhuhai Campus), Zhuhai 519082, China.
⁶ School of Mathematical Sciences, Fudan University, Shanghai 200433, China.
⁷ National Engineering Research Center of Electromagnetic Radiation Control Materials, School of Electronic Science and Engineering, University of Electronic Science and Technology of China, Chengdu 611731, China.
⁸ School of Physical Sciences, University of Chinese Academy of Sciences, Beijing 100049, China.
⁹ Department of Physics, National University of Singapore, 2 Science Drive 3, Singapore 117542, Singapore.

PMID: 34928607
DOI: 10.1021/acs.nanolett.1c03622

Abstract

The burgeoning field of twistronics, which concerns how changing the relative twist angles between two materials creates new optoelectronic properties, offers a novel platform for studying twist-angle dependent excitonic physics. Herein, by surveying a range of hexagonal phase transition metal dichalcogenides (TMD) twisted homobilayers, we find that 21.8 ± 1.0°-twisted ( $\sqrt{7} a \times \sqrt{7} a$ ) and 27.8 ± 1.0°-twisted ( $\sqrt{13} a \times \sqrt{13} a$ ) bilayers account for nearly 20% of the total population of twisted bilayers in solution-phase restacked bilayers and can be found also in chemical vapor deposition (CVD) samples. Examining the optical properties associated with these twisted angles, we found that 21.8 ± 1.0° twisted MoS₂ bilayers exhibit an intense moiré exciton peak in the photoluminescence (PL) spectra, originating from the refolded Brillouin zones. Our work suggests that commensurately twisted TMD homobilayers with short commensurate wavelengths can have interesting optoelectronic properties that are different from the small twist angle counterparts.

Keywords: Twistronics; commensuration; moiré excitons; scanning transmission electron microscopy; twisted 2D homobilayers.