  Excitons in two-dimensional transition metal dichalcogenides have a valley
degree of freedom that can be optically accessed and manipulated for quantum
information processing. Here, we integrate MoS2 with achiral silicon disk array
metasurfaces to enhance and control valley-specific absorption and emission.
Through the coupling to the metasurface Mie modes, the intensity and lifetime
of the emission of neutral excitons, trions and defect bound excitons can be
enhanced, while the spectral shape can be modified. Additionally, we
demonstrate the symmetric enhancement of the degree-of-polarization (DOP) of
neutral exciton and trions via valley-resolved PL measurements, and find that
the DOP can be as high as 24% for exciton emission and 34% for trion emission
at 100K. These results can be understood by analyzing the near-field impact of
metasurface resonators on both the chiral absorption of MoS2 emitters as well
as the enhanced emission from the Purcell effect. Combining Si-compatible
photonic design with large-scale (mm-scale) 2D materials integration, our work
makes an important step towards on-chip valleytronic applications approaching
room-temperature operation.
