2D transition metal dichalcogenides (TMDCs) are monolayer semiconductors with a lot of interesting optoelectronic properties. Most 2D TMDCs present a direct band gap in the visible and render the excitons with large excitonic binding energy when interacting with photons, an excellent material platform for excitonic devices. Besides, the broken time reversal symmetry of the atomic structures induces the opposite Berry curvatures and pseudo-spins in the electronic band structures, lifting the valley degeneracy and resulting in a valley-contrast absorption and emission of spin-photons. Moreover, their broken inversion symmetry could allow the strong photonic spin-dependent second-harmonic generation (SHG), coupled to the interband transition in different valleys. Hybridizing the metasurface with 2D TMDCs can help to address those exciting properties of 2D TMDCs. In my research, we mainly aim to investigate to integrate the linear metasurfaces with nonlinear monolayer semiconductors. Particularly, we have achieved:

• through the coherent SHG, the emitted chiral photons from opposite valleys of 2D TMDCs, boosted by the strong plasmonic field localization, could be controllably separated and steering to different directions, leading to free-space and room-temperature valleytronic and nonlinear photonic devices [1];

• a nonlinear interface made of metasurface and 2D TMDCs has been built for multifunctional metaphotonics applications. We demonstrate the fully controllable polarization state of SHG, the tunable SHG orbit angular momentum generator, the tunable beam steering of SHG and nonlinear holography by reshaping the emissions of monolayer semiconductors [2].

In the future, we aim to demonstrate (1). the quantum metasurface in nonlinear regime, (2) the topological light and (3) the valley-excitonic devices out of this exciting platform for various applications including the advanced quantum and topological light source, the hybrid nonlinear devices, the valleytronic andexcitonic nanodevices.

[1]. Nature Photonics 13, 467-472, (2019)

[2]. Research, 2020, 9085782, (2020)