Two-dimensional transition-metal dichalcogenides (TMDCs) exhibit extraordinary nonlinearities and direct bandgaps at K (K') valleys. Those valleys could be optically manipulated through the plasmon-valley-exciton coupling, for example, with spin-dependent photoluminescence. However, the weak coherence between the pumping and emission due to intervalley scattering poses formidable challenges in exploring the valley-contrasting physics and applications. Here we show that a synthetic metasurface entangling the phase and spin of light can simultaneously enhance and manipulate the nonlinear valley-locked chiral emission in monolayer tungsten disulfide (WS 2) at room temperature. The second-harmonic valley photons, accessed and coherently pumped by the light with spin-related geometric phase imparted by Au-metasurface, are separated and routed to predetermined directions in free space. Besides, the nonlinear photons with the same spin of incident light can be steered into any predefined direction thanks to the nonlinear optical selection rule of WS 2 in our synthetic metasurface. Our synthetic TMDCs-metasurface interface may facilitate advanced roomtemperature and free-space nonlinear, quantum and valleytronic nanodevices.

Organic-inorganic perovskites have attracted great attentions driven by exceptional progress in photovoltaics, photonics and optoelectronics. Different from the corner sharing framework of three-dimensional (3D) perovskite, two-dimensional (2D) organic-inorganic perovskites possess a layered staking structure composed of alternative organic and inorganic components.Due to the inherent multi-quantum-well-like structure, it is intriguing to explore the optical properties of 2D perovskites enabled by spatial and dielectric confinement. Herein, the twophoton absorption (TPA) properties of 2D perovskite phenylethylamine lead iodide ((PEA)2PbI4) are systematically studied. The 2D perovskite exhibits a giant TPA and saturation effect under excitation of 800 nm femtosecond laser. The TPA coefficient of a (PEA)2PbI4 flake is measured to be about 211.5 cm/MW, which is at least one order of magnitude larger than those of 3D perovskite films and some typical semiconductor Submitted to 2 2 nanostructures. The giant TPA can be attributed to the enhanced quantum and dielectric confinement in the organic-inorganic multi-quantum-well structure. In addition, a highly thickness-dependent TPA is observed for the 2D perovskite flakes. The result advocates a great promise of 2D organic-inorganic perovskites for nonlinear optical absorption related optoelectronic devices.