Intensity, wavelength and polarization control of valley excitonic emissions in monolayer MoS₂ by dielectric metasurfaces

Transition metal dichalcogenide (TMDC) monolayers host robust excitons with a valley degree of

freedom that can be optically accessed with circularly polarized light. Here, we demonstrate intensity,

wavelength and polarization control of valley excitonic emission in monolayer MoS 2 by coupling MoS 2

with dielectric metasurfaces composed of arrays of silicon nano-disks. By varying the disk diameter, we

are able to tune the frequencies of Mie scattering modes of the disks to match the exciton frequency in

MoS 2 . The photoluminescence (PL) intensity of MoS 2 can be enhanced by more than 30x on the

metasurface compared with the response for the monolayer on a flat substrate as a consequence of

both excitation and emission enhancement by the metasurface modes. The spectral distribution of the

MoS 2 emission can be markedly modified by the coupling of neutral excitons, trions, and defect bound

excitonic states with the resonance of the metasurfaces. The measured degree of circular polarization of

PL emission exhibits a clear dependence on the metasurface modes because of the Purcell effect, which

is also substantiated by PL lifetime measurements. We will discuss the experimental results and how

they can be understood in terms of electromagnetic simulations of the metasurface response.