Dynamically tunable moiré exciton Rydberg states in a monolayer semiconductor on twisted bilayer graphene

Minhao He; Jiaqi Cai; Huiyuan Zheng; Eric Seewald; Takashi Taniguchi; Kenji Watanabe; Jiaqiang Yan; Matthew Yankowitz; Abhay Pasupathy; Wang Yao; Xiaodong Xu

doi:10.1038/s41563-023-01713-y

Dynamically tunable moiré exciton Rydberg states in a monolayer semiconductor on twisted bilayer graphene

Nat Mater. 2024 Feb;23(2):224-229. doi: 10.1038/s41563-023-01713-y. Epub 2024 Jan 4.

Authors

Minhao He^#¹, Jiaqi Cai^#¹, Huiyuan Zheng^#², Eric Seewald³, Takashi Taniguchi⁴, Kenji Watanabe⁵, Jiaqiang Yan^{6

7}, Matthew Yankowitz^{1

8}, Abhay Pasupathy³, Wang Yao^{9

10}, Xiaodong Xu^{11

12}

Affiliations

¹ Department of Physics, University of Washington, Seattle, WA, USA.
² Department of Physics, University of Hong Kong, Hong Kong, China.
³ Department of Physics, Columbia University, New York, NY, USA.
⁴ International Center for Materials Nanoarchitectonics, National Institute for Materials Science, Tsukuba, Japan.
⁵ Research Center for Functional Materials, National Institute for Materials Science, Tsukuba, Japan.
⁶ Materials Science and Technology Division, Oak Ridge National Laboratory, Oak Ridge, TN, USA.
⁷ Department of Materials Science and Engineering, University of Tennessee, Knoxville, TN, USA.
⁸ Department of Materials Science and Engineering, University of Washington, Seattle, WA, USA.
⁹ Department of Physics, University of Hong Kong, Hong Kong, China. wangyao@hku.hk.
¹⁰ HKU-UCAS Joint Institute of Theoretical and Computational Physics at Hong Kong, Hong Kong, China. wangyao@hku.hk.
¹¹ Department of Physics, University of Washington, Seattle, WA, USA. xuxd@uw.edu.
¹² Department of Materials Science and Engineering, University of Washington, Seattle, WA, USA. xuxd@uw.edu.

^# Contributed equally.

PMID: 38177379
DOI: 10.1038/s41563-023-01713-y

Abstract

Moiré excitons are emergent optical excitations in two-dimensional semiconductors with moiré superlattice potentials. Although these excitations have been observed on several platforms, a system with dynamically tunable moiré potential to tailor their properties is yet to be realized. Here we present a continuously tunable moiré potential in monolayer WSe₂, enabled by its proximity to twisted bilayer graphene (TBG) near the magic angle. By tuning local charge density via gating, TBG provides a spatially varying and dynamically tunable dielectric superlattice for modulation of monolayer WSe₂ exciton wave functions. We observed emergent moiré exciton Rydberg branches with increased energy splitting following doping of TBG due to exciton wave function hybridization between bright and dark Rydberg states. In addition, emergent Rydberg states can probe strongly correlated states in TBG at the magic angle. Our study provides a new platform for engineering moiré excitons and optical accessibility to electronic states with small correlation gaps in TBG.