Spatial separation of valley exciton emissions from monolayer MoS₂ through spin-orbit coupling of light

Chien-Ju Lee^1*, Chih-Lun Wu¹, Li-Shuan Lu¹, Wen-Hao Chang¹

¹Electrophysics, National Chiao Tung University, Hsinchu, Taiwan

* Presenter:Chien-Ju Lee, email:Chienju1016@gmail.com

Valleytronics utilizes the valley degree of freedom of carriers to carry information, in analogy to electric charge and spin of electrons. Due to the unique coupled spin-valley properties of two-dimensional (2D) transition metal dichalcogenides (TMDs), these materials exhibit valley contrast optical selection rule and have triggered intense research activities in realizing valleytronic applications. In this work, we demonstrate the coupling of monolayer MoS₂ with the surface plasmon-polariton (SPP) of a periodic plasmonic structure to achieve spatial separation of valley-polarized exciton emissions at room temperature. Spin-orbit coupling of light in nano-photonic and plasmonic structures have been used to separate propagation path of photons with different spins. In the coupled MoS₂-plasmonic structure, SPP waves excited by exciton emissions with opposite helicities interact with the periodic metallic structure and routed into different directions. Through polarization-resolved photoluminescence imaging in both real and momentum space for the coupled MoS₂-plasmonic structure, we observed valley-dependent directional coupling of exciton emissions when the excitons are on resonance with the SPP mode. The direction of each SPP propagation is determined by the period of the plasmonic structure. Our results demonstrate a feasible way for optically controlling and detecting the exciton valley polarization in TMDs.

Keywords: 2D materials, transition metal dichalcogenides, device applications