Observation of the polaronic character of excitons in a two-dimensional semiconducting magnet CrI3

Wencan Jin; Hyun Ho Kim; Zhipeng Ye; Gaihua Ye; Laura Rojas; Xiangpeng Luo; Bowen Yang; Fangzhou Yin; Jason Shih An Horng; Shangjie Tian; Yang Fu; Gongjun Xu; Hui Deng; Hechang Lei; Adam W Tsen; Kai Sun; Rui He; Liuyan Zhao

doi:10.1038/s41467-020-18627-x

Observation of the polaronic character of excitons in a two-dimensional semiconducting magnet CrI₃

Nat Commun. 2020 Sep 22;11(1):4780. doi: 10.1038/s41467-020-18627-x.

Authors

Wencan Jin^{1

2}, Hyun Ho Kim^{3

4}, Zhipeng Ye⁵, Gaihua Ye⁵, Laura Rojas⁵, Xiangpeng Luo¹, Bowen Yang³, Fangzhou Yin³, Jason Shih An Horng¹, Shangjie Tian⁶, Yang Fu⁶, Gongjun Xu⁷, Hui Deng¹, Hechang Lei⁶, Adam W Tsen³, Kai Sun¹, Rui He⁸, Liuyan Zhao⁹

Affiliations

¹ Department of Physics, University of Michigan, 450 Church Street, Ann Arbor, MI, 48109, USA.
² Department of Physics, Auburn University, 380 Duncan Drive, Auburn, AL, 36849, USA.
³ Institute for Quantum Computing, Department of Chemistry, and Department of Physics and Astronomy, University of Waterloo, Waterloo, 200 University Ave W, Ontario, N2L 3G1, Canada.
⁴ School of Materials Science and Engineering, Kumoh National Institute of Technology, Gumi, Gyeongbuk, 39177, Korea.
⁵ Department of Electrical and Computer Engineering, 910 Boston Avenue, Texas Tech University, Lubbock, TX, 79409, USA.
⁶ Department of Physics and Beijing Key Laboratory of Opto-electronic Functional Materials & Micro-nano Devices, Renmin University of China, Beijing, 100872, China.
⁷ Department of Statistics, University of Michigan, 1085 South University, Ann Arbor, MI, 48109, USA.
⁸ Department of Electrical and Computer Engineering, 910 Boston Avenue, Texas Tech University, Lubbock, TX, 79409, USA. [email protected].
⁹ Department of Physics, University of Michigan, 450 Church Street, Ann Arbor, MI, 48109, USA. [email protected].

Abstract

Exciton dynamics can be strongly affected by lattice vibrations through electron-phonon coupling. This is rarely explored in two-dimensional magnetic semiconductors. Focusing on bilayer CrI₃, we first show the presence of strong electron-phonon coupling through temperature-dependent photoluminescence and absorption spectroscopy. We then report the observation of periodic broad modes up to the 8th order in Raman spectra, attributed to the polaronic character of excitons. We establish that this polaronic character is dominated by the coupling between the charge-transfer exciton at 1.96 eV and a longitudinal optical phonon at 120.6 cm^-1. We further show that the emergence of long-range magnetic order enhances the electron-phonon coupling strength by ~50% and that the transition from layered antiferromagnetic to ferromagnetic order tunes the spectral intensity of the periodic broad modes, suggesting a strong coupling among the lattice, charge and spin in two-dimensional CrI₃. Our study opens opportunities for tailoring light-matter interactions in two-dimensional magnetic semiconductors.

Abstract

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