Abstract
Transition metal dichalcogenide (TMDC) monolayers have enabled important applications in light emitting devices and integrated nanophotonics because of the direct bandgap, spin-valley locking and highly tunable excitonic properties. Nevertheless, the photoluminescence polarization is almost random at room temperature due to the valley decoherence. Here, we show the room temperature control of the polarization states of the excitonic emission by integrating WS2 monolayers with a delicately designed metasurface, i.e. a silver sawtooth nanoslit array. The random polarization is transformed to linear when WS2 excitons couple with the anisotropic resonant transmission modes that arise from the surface plasmon resonance in the metallic nanostructure. The coupling is found to enhance the valley coherence that contributes to ~30% of the total linear dichroism. Further modulating the transmission modes by optimizing metasurfaces, the total linear dichroism of the plasmon-exciton hybrid system can approach 80%, which prompts the development of photonic devices based on TMDCs.
Highlights
Transition metal dichalcogenide (TMDC) monolayers have enabled important applications in light emitting devices and integrated nanophotonics because of the direct bandgap, spinvalley locking and highly tunable excitonic properties
TMDCs implemented in plasmon-exciton hybrid systems have been intensively explored, such as giant Rabi splitting[27,28], multifold enhancement in PL29,30 and active control of plasmon-exciton coupling[31,32] in various noble metal-TMDC
For bare TMDCs, the linearly polarized emission can only be generated by a coherent superposition of two circularly polarized photons from K and K' valleys[41], and the polarization direction can be controlled by the magnetic field induced valley Zeeman splitting effect[42]
Summary
Transition metal dichalcogenide (TMDC) monolayers have enabled important applications in light emitting devices and integrated nanophotonics because of the direct bandgap, spinvalley locking and highly tunable excitonic properties. The random polarization is transformed to linear when WS2 excitons couple with the anisotropic resonant transmission modes that arise from the surface plasmon resonance in the metallic nanostructure. The highly efficient growth by chemical vapor deposition (CVD) is promising to meet the demand of mass production[11] Benefiting from these advantages, TMDCs offer a unique platform for investigation of intriguing light-matter interactions at the nanoscale through, besides the well-known van der Waals heterostructures[12,13], the integration with artificial materials, such as photonic nanocavities[14,15], plasmonic nanostructures[16], and single nanoparticle antennas[17]. The plasmonic metasurface—the broadband and ultrafast plasmonic cavity—is proposed to suppress the quantum decoherence by enhancing the light-matter interactions, which is essential to preserve the linear polarization of the valley excitons at room temperature[43]. The optical mode needs to couple with the excitation field, so that the pump energy can be absorbed efficiently by the TMDC monolayers buried underneath the metallic structure
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