Manipulating Light-Matter Coupling in Monolayer Semiconductors by Photonic and Plasmonic Structures
Wen-Hao Chang1*
1Department of Electrophysics, National Chiao Tung University, Hsinchu, Taiwan
* Presenter:Wen-Hao Chang
Two-dimensional (2D) semiconductors, particularly the direct-gap monolayer transition metal dichalcogenides (TMDs), have emerged as a new optically-active materials for developing various atomically-thin photonic and optoelectronic applications. However, practical applications are hindered by their low quantum efficiencies in light emissions and absorptions. Tailoring the light-matter coupling in 2D semiconductors becomes a crucial route not only for improving the device performance, but also for exploring a novel way to manipulate the strong excitonic effects and the spin-valley dependent properties. In this talk, I will present our recent endeavors on manipulating the light-matter coupling in 2D TMDs using photonic and plasmonic structures. Firstly I will show that a suitably designed distributed Bragg reflector (DBR) can be an ideal platform for light-coupling enhancement, such as photoluminescence (PL), Raman and second harmonic generation (SHG) in 2D TMDs. In particular, the giant SHG enhancement by the monolayer TMDs on DBR is successfully applied to the technique of frequency-resolved optical grating for characterizing spectral phase of low-light-level ultrafast pulses. Secondly I will demonstrate the controlled light-matter coupling in monolayer TMDs by plasmonic grating structures. The surface-plasmon-polariton (SPP) resonance combined with the plasmonic gap mode can strongly couple with the excitons in monolayer MoS2. A Rabi splitting up to 68 meV has been achieved at room temperature for the 2D plasmon-exciton polariton, which open up the possibility to realize high-temperature polariton condensates. Finally, I will show that plasmonic chiral structures can be used to manipulate valley polarization in monolayer MoS2. The plasmonic chiral structure can create a helicity-dependent optical density of states, which in turn lead to a valley-dependent carrier decay dynamics, giving rise to a high degree of circularly polarized PL even at room temperature. Our results demonstrate a route for tailoring the valley-dependent carrier dynamics, which can be utilized in valley-based optoelectronic applications based on monolayer TMDs.

Keywords: light-matter interaction, transition metal dichalcogenides, strong coupling