Institute Colloquium

Prof. Shun-Jen Cheng

Selective Photo-excitation and Angular Momentum Imprint of Exciton Complexes in 2D Materials by Using Twisted Lights

October 9, 2024

Start: 2-4 pm

Venue: Conference room at Leibniz IPHT

Contact person: Jer-Shing Huang

Prof. Shun-Jen Cheng works ans the Department of Electrophysics at National Yang Ming Chiao Tung University. His aereas of interest are many-body theory in semiconductor nanosctrustures, exciton physics in 2D materials, structured lights and their interactions with excitons as well as nanophotonics. He earned his PhD from the University of Würzburg in 2001. Before that he obtained his Masters degree at the Institute of Electrical engineering at National Taiwan University in Taipei/Taiwan and his Bachelors degree in Hsinchu/Taiwan at the Department of Electrical engineering at National Tsing-Hua University.

Twisted light is a type of specially structued light where the wavefront is spatially twisted so as to acquire orbital angular momenta (OAM), being a new degree of freedom of light in addition to that of spin angular momentum (SAM), i.e. polarization. Inetrestingly, the quantum number of the optical OAM carried by a TL, unlike SAM, can be an arbitray integer so that TL-based photonics is prospective for the realizing the high-capacity quantum information technology and high dimensional quantum entangled states.

In the presentation, I will review our recent theory-experiment-joint studies of the light-matter interactions between excitons in atomically thin transition-metal dichalcogenide (TMD) monolayers and spatially structured lights, including twisted lights (TLs) carrying orbital angular momenta (OAM) and spin-orbit-coupled vector vortex beams (VVB). [1-3] Theoretically, we developed the theory of light-matter interaction between 2D excitons and TLs within the framework of first-principles-based Bethe Salpeter equation (BSE) and time-dependent perturbation theory. The theory explains the observed PL blue-shifts of a hBN-encapsulated MoS₂-ML under the excitation of TL with controlled OAM, as a consequence of TL-selective photo-excitation of finite momentum excitons.

References
[1] K. B. Simbulan, T.-D. Huang, G.-H. Peng, F. Li, O. J. G. Sanchez, J.-D. Lin, C.-I Lu, C.-S. Yang, J. Qi, S.-J. Cheng, T.-H. Lu, and Y.-W. Lan, ACS Nano 15, 3481–3489 (2021).
[2] 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. 19, 2299–2312 (2019).
[3] G.-H. Peng, O. J. G. Sanchez, W.-H. Li, P.-Y. Lo, and S.-J. Cheng, Phys. Rev. B 106, 155304 (2022).

The lecture will be given in English.