Bright and dark exciton band engineering of monolayer MoS₂ by applying uniaxial strain

Ching-Hung Shih^1*, Wei-Hua Li², Mei-Ling Xu², Chao-Hsin Chien¹, Shun-Jen Cheng²

¹Institute of Electronics, National Yang Ming Chiao Tung University, Hsinchu City, Taiwan
²Department of Electrophysics, National Yang Ming Chiao Tung University, Hsinchu City, Taiwan

* Presenter:Ching-Hung Shih, email:shih2356585@gmail.com

Numerous studies have pointed out that monolayer MoS₂ exhibits valley drift after the application of strain¹. This phenomenon significantly impacts the electronic band structure and subsequently influences the exciton energy band structure,which have been observed by photoluminescence spectroscopy(PL)². Therefore, the primary focus of this article is to investigate how the exciton energy bands and their corresponding dipoles are influenced after the application of different strain intensities from 10% compressive to 10% tensile and how they are affected by the electronic band structure and Coulomb interaction.
Starting with a first-principles-based Bethe-Salpeter equation(BSE) approach³, we find that, even though valley drift has a dramatic effect on the electronic band structure, the energy bands of bright excitons are predominantly governed by exchange energy, leading to the occurrence of an anticrossing phenomenon. At the anticrossing point, the exciton's polarization rapidly transitions from linear to circular and then back to its original linear polarization. This result suggests that we can control the luminescent polarization of MoS₂ by applying strain.

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2. N. Jena, Dimple, R. Ahammed, A. Rawat, M. K. Mohanta, and A. D. Sarkar, Phys. Rev. B. 2019, 100, 165413.
3. G. H. Peng, P. Y. Lo, W. H. Li, Y. C. Huang, Y. H. Chen, C. H. Lee, C. K. Yang, and S. J. Cheng, Nano Lett. 2019, 19, 2299.

Keywords: Monolayer MoS₂, uniaxial strain, valley drift, Bright exciton, Dark exciton