Dynamic Spin-Decoupled Terahertz Metasurfaces via Graphene-Metal Asymmetric Coupling

The dynamic integration of chiral optical responses and complex vector light fields within a single ultracompact platform remains challenging due to the intrinsic spin-conjugate symmetry of conventional metasurfaces. In this work, we propose an electrically reconfigurable terahertz (THz) metasurface based on graphene-metal hybrid asymmetric resonators that fundamentally break this spin-locking constraint. By tuning the Fermi level of graphene via electrostatic gating, the device enables on-demand switching between distinct optical functionalities with high contrast. At a low Fermi level ( E_F=0.01\text eV), the metasurface operates as a broadband half-wave plate, efficiently converting orthogonal linearly polarized waves into high-purity higher-order vector vortex beams with a polarization order of m=2 . Conversely, at a high Fermi level (E_F=0.7\text eV) , the increased conductivity of graphene induces strong asymmetric near-field coupling, transforming the metasurface into a chiral mirror. At this state, the device exhibits giant circular dichroism with a reflectance contrast exceeding 0.9, acting as a near-perfect absorber for right-handed circularly polarized (RCP) light, while selectively reflecting left-handed circularly polarized light into an RCP vortex beam carrying a topological charge of l=+2 . This work provides a practical and highly programmable paradigm for the active and synergistic manipulation of spin and orbital angular momentum, holding great promise for next-generation THz communications, multidimensional biosensing, and reconfigurable photonic systems.