  Recent advances in condensed matter physics have shown that the valley degree
of freedom of electrons in 2D materials with hexagonal symmetry, such as
graphene, h-BN, and TMDs, can be efficiently exploited, leading to the emergent
field of valleytronics, which offers unique opportunities for efficient data
transfer, computing and storage. The ability to couple the valley degree of
freedom of electrons with light can further expand the ways one manipulate this
degree of freedom, thus envisioning a new class of solid-state-photonic
interfaces and devices. Besides this expansion of control of valley by
light-waves, coupling of photons with valley-polarized electrons can
dramatically expand the landscape of available optical responses, which may
bring new means of controlling light in photonic devices. In this work we
design such hybrid solid-state photonic metasurface integrating 2D TMD and
photonic all-dielectric metasurface. While TMD is naturally endowed with the
property of valley to optical-polarization coupling, the photonic metasurface
is designed to produce chiral field which selectively couples to the valley
degree of freedom of solid-state TMD component. We experimentally demonstrate
that such coupling leads to controlled valley polarization due to the coupling
of 2D materials with the chiral photonic metasurface. The measured emission
from valley excitons in this hybrid system yields the preferential emission of
specific helicity.
