Polarization‐Sensitive Enhancement of Photoluminescence and Interlayer Absorption in WSe₂/InSe Heterostructure via Plasmonic Metastructure

2D van der Waals heterostructures (vdWH) serve as ideal platforms for studying interlayer excitons (IX) and developing excitonic devices. Typically, IX exhibit in-plane isotropy and weak oscillator strengths, limiting their application in high-performance and polarization-sensitive optoelectronics. In this work, through the coupling of plasmonic resonances to multilayer WSe₂/InSe vdWH, both anisotropy and enhancement of IX emissions are achieved thanks to the specifically designed metastructure, which couples plasmonic resonance modes with the excitation field in the visible and aligns with the excitonic emission in the near-infrared (NIR). By harnessing the significantly enhanced electromagnetic field generated by the anisotropic plasmonic resonance, a remarkable 52-fold increase is achieved in IX emission intensity, accompanied by an anisotropic ratio of 23%. Furthermore, by utilizing the polarization-sensitive and enhanced interlayer absorption, a NIR WSe₂/InSe photodetector is fabricated on the metastructure, achieving a linear polarization ratio of 5.2 along with an optimal photoresponsivity of 1.85 mA W^-1 at 1120 nm, one order of magnitude higher than the pristine WSe₂/InSe photodetector. This work provides a universal approach for introducing anisotropy into IX, while simultaneously enhancing the IX emission and interlayer absorption in 2D vdWH.