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Physics Seminar

Excitons and Exciton Polaritons in Van der Waals Semiconductors

Speaker: Prof Long Zhang (Xiamen University)
Date: Friday 27 November 2020
Time: 11:00 in UK
Venue: Zoom

Van der Waals Semiconductors such as transition metal dichalcogenides (TMDs) mark a new frontier for condense matter physics and the optoelectronics. The two-dimensionality of the monolayer TMDs and weak dielectric screening yield a significant enhancement of the Coulomb interaction. As a result, the optical properties of TMDs are widely dominated by excitons, Coulomb-bound electron–hole pairs. With high exciton binding energy, large exciton oscillator strength, and unprecedented integration flexibility with optical architectures, TMDs provide a new platform to study exciton polaritons, a new quasi-particle formed by strong coupling between an exciton and a photon. In this talk, I will begin with the excitons polaritons in TMDs monolayers coupled with a one-dimensional photonic crystal [1]. Then I will introduce two types of TMDs heterobilayers and talk about how the properties of excitons are controlled by heterostructures [2,3]. Lastly, these two types of heterobilayers are integrated with optical cavities, which give rise to exciton-photon interactions in weak and strong coupling regimes respectively [4].

1. Zhang, L., Gogna, R., Burg, W., Tutuc, E. & Deng, H. Photonic-crystal exciton-polaritons in monolayer semiconductors. Nature Communications 9, 1–8 (2018). 2. Zhang, L. et al. Highly valley-polarized singlet and triplet interlayer excitons in van der Waals heterostructure. Phys. Rev. B 100, 041402 (2019). 3. Zhang, L. et al. Twist-angle dependence of moiré excitons in WS 2 /MoSe 2 heterobilayers. Nature Communications 11, 5888 (2020). 4. Paik, E. Y*. Zhang, L*. et al. Interlayer exciton laser of extended spatial coherence in atomically thin heterostructures. Nature 576, 80–84 (2019).