Unraveling the Linear Energy Dispersion in Monolayer MoS₂ using Twisted Light with Orbital Angular Momentum

Kristan Bryan Simbulan^1*, Teng-De Huang¹, Guan-Hao Peng², Feng Li³, Oscar Javier Gomez Sanchez², Jhen-Dong Lin², Junjie Qi³, Shun-Jen Cheng², Ting-Hua Lu¹, Yann-Wen Lan¹

¹Department of Physics, National Taiwan Normal University, Taipei, Taiwan
²Department of Electrophysics, National Chiao Tung University, Hsinchu, Taiwan
³School of Materials Science and Engineering, University of Science and Technology Beijing, Beijing, China

* Presenter:Kristan Bryan Simbulan, email:80641005s@ntnu.edu.tw

Owing to its reduced dielectric screening, two-dimensional (2D) transition metal dichalcogenides (TMDs) materials exhibit an optical response that is dominated by tightly-bound electron-hole pairs, called excitons, even at room temperature. It has been predicted in recent theoretical works that a peculiar low-energy exciton dispersion in monolayer (ML) MoS₂ – a prototypical TMD, consisting of a dominant linear v-shaped upper band and a parabolic lower band, at zero center-of-mass momentum exists due to the electron-hole exchange interaction in the material. Our work presents an experimental evidence of this unusual excitonic property by analyzing the photoluminescence (PL) spectra of the material excited by twisted light with orbital angular momentum. Our experimental results indicate a blue shift in the PL spectra of the ML-MoS₂ as the topological charge of the incident twisted light is incremented along its positive and negative values, which is in good agreement with our numerical simulations. Notably, the non-linear topological charge-dependence pattern formed by these spectral shifts is shown to be associated with the predicted dominant linear exciton band of the single-layer MoS₂. This study thus presents experimental process and findings that provide new knowledge that will trigger further developments in the emerging field of 2D TMD materials.

Keywords: twisted light, linear exciton dispersion, light-matter interaction, transition metal dichalcogenides, orbital angular momentum