Valley selective optical control of excitons in 2D semiconductors using a chiral metasurface [Invited]
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.