Imaging the Exciton Orientation in Bilayer WS2/MoS2 by Momentum-Resolved Photoluminescence
Wei-Ting Hsu1*, Po-Hsun Wu1, Li-Syuan Lu1, Yi-Chia Chou1, Lain-Jong Li2, Wen-Hao Chang1
1Department of Electrophysics, National Chiao Tung University, Hsinchu, Taiwan
2Physical Sciences and Engineering, King Abdullah University of Science and Technology, Thuwal, Saudi Arabia
* Presenter:Wei-Ting Hsu,
Excitons, the Coulomb-bound electron-hole pairs, play a very important role in the optical properties of two-dimensional transition metal dichalcogenides (TMDs). Inheriting from the atomically thin thickness, the intralayer excitons have been demonstrated with giant binding energy, strong many-body effects, and the nonhydrogenic Rydberg excited states. Apart from these established properties, the orientations of exciton dipole are seldom discussed but rather important for the design of TMD-based photonic devices, which determine the emission direction and coupling strength. In the past, the intralayer excitons in monolayer MoS2 have been demonstrated with strong horizontal dipoles and negligible vertical dipoles. Orientations of interlayer excitons in bilayer TMD heterostructures, on the other hand, remain largely unexplored due to the vertical separation of electrons and holes by the type-II interfaces. Here, the dipole orientations of interlayer excitons in bilayer WS2/MoS2 heterojunction were investigated by the momentum-resolved photoluminescence spectra. In contrary to the horizon-oriented intralayer excitons, we observed strong horizontal and vertical dipole components for interlayer excitons. The relative dipole moments between horizontal and vertical dipoles were further determined by the analytical calculations and examined by the wave function simulations. The strong out-of-plane dipoles of interlayer excitons in bilayer TMD heterostructure thus provide a brand-new building block for the planar photonic circuits and are very promising for integrating with plasmonics structures.

Keywords: transition metal dichalcogenides, van der Waals heterostructure, interlayer exciton, Fourier plane microscopy