We report the magnetic proximity effect (MPE) and valley non-degeneracy in monolayer MoS and magnetic semiconductor EuS thin film heterojunctions studied by density functional theory (DFT) with the vdW-DF2 correlations. Magnetic moments are observed in MoS due to the MPE when forming chemical or van der Waals (vdW) adsorption states with EuS. Spin-orbit coupling (SOC) leads to observable valley non-degeneracy of MoS at the K (K') points in the Brillouin zone. The valley Zeeman splitting energy E can reach 5.1 meV and 37.3 meV for the vdW and chemical adsorption states, corresponding to a magnetic exchange field (MEF) of 22 T and 160 T respectively. By applying a gate voltage across the MoS/EuS interface, it is found that E can be tuned from 1.8 meV to 8.2 meV and from 24.5 meV to 53.8 meV for vdW and chemical adsorption states respectively. The strong MPE, large and tunable valley degeneracy in 2D material and ferromagnetic semiconductor/insulator vdW heterojunctions demonstrate their promising potential for novel optoelectronic and valleytronic device applications.

Chiral nanophotonic devices are promising candidates for chiral molecules sensing, polarization diverse nanophotonics and display technologies. Active chiral nanophotonic devices, where the optical chirality can be controlled by an external stimulus has triggered great research interest.However, efficient modulation of the optical chirality has been challenging. Here, we demonstrate switching of the extrinsic chirality by applied magnetic fields in a magneto-plasmonic metasurface device based on a magneto-optical oxide material, Ce1Y2Fe5O12 (Ce:YIG). Thanks to the low optical loss and strong magneto-optical effect of Ce:YIG, we experimentally demonstrated a giant and continuous far-field circular dichroism (CD) modulation by applied magnetic fields from -0.65° to +1.9° at 950 nm wavelength under glancing incident conditions. The far field CD modulation is due to both magneto-optical circular dichroism and near-field modulation of the superchiral fields by applied magnetic fields. Finally, we demonstrate magnetic field tunable chiral imaging in millimeter-scale magneto-plasmonic metasurfaces fabricated using self-assembly. Our results 2 provide a new way for achieving planar integrated, large-scale and active chiral metasurfaces for polarization diverse nanophotonics. KEYWORDS: Magnetoplasmonic, Metasurface, Optical Chirality, Magneto-optical effectChirality describes the symmetry property of a structure, that its mirror image cannot be superimposed with itself through translation and rotation operations, like our two hands. The chirality of biomolecules is universal in our living body, such as amino acid and proteins, which has significance in biomolecules recognition. 1,2 However, the chiroptical signal of chiral biomolecules is very weak. Recently, chiral plasmonic 3,4 and all dielectric structures 5,6 with large chiroptical response have attracted great research interest. Benefitted from advanced nano-fabrication technologies, 3D or planar chiroptical nanostructures, such as helices, 7,8 shurikens, 9 gammadions, 6,10 and twisted split-rings 11 have been fabricated. On the other hand, extrinsic chirality can also be observed in achiral photonic nanostructures under obliquely incidence conditions. The extrinsic chirality is originated from asymmetric distributions of electromagnetic fields, i.e. the electromagnetic near field distribution is chiral. 12 Nanophotonic structures such as nanoholes, 12 squares 13 and split ring resonators 14,15 showed large extrinsic chirality. For instance, Ben et al.demonstrated a ~4 times stronger optical chirality in achiral periodic nanoholes compared to the gammadion structure. 12 Recently, Abraham et. al. experimentally demonstrated that the achiral nanohole structures can also show superchiral near-fields even at perpendicular incidence conditions. 16 In that case, the far-field circular dichroism (CD) background signals from the plasmonic structures is eliminated, improving the sensitivity for chiral molecule sensing applications. These reports demonstrate a promising potent...

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The generation and manipulation of vector light fields are of great significance for both fundamental research and industrial applications of polarized optics. In recent years, the spatial domain control of structured vector fields has gradually expanded from two-to three-dimensional, including traditional optics and meta-optics. Here, a new method to generate and manipulate structured vector light fields along the propagation direction is proposed, and the functionality in terahertz band using all-silicon metasurfaces is demonstrated. The coherent superposition of orthogonal circularly polarized terahertz waves through long focal depth and multifocal metalens is completed, and varying phase differences between them in the propagation direction via path accumulation or initial phase design are introduced, thereby continuous variation or independently designed vector polarization distributions in multiple planes are obtained. It is worth mentioning that the proposed scheme is not only for the design of transverse electric field components, but also shows a strong ability for manipulation of the longitudinal component. This scheme realizes the polarization distribution designs of three-dimensional vector fields in three-dimensional space, and provides a new inspiration for the generation and manipulation of vector beams based on meta-optics.