Broadband fully spin-polarized and pure spin currents driven by the photogalvanic effect in half-metallic ScSi2N4

Using first-principles calculations combined with the nonequilibrium Green's function formalism, we investigate the spin-dependent photogalvanic transport driven by the second-order nonlinear photogalvanic effect in monolayer half-metallic ScSi 2 N 4 . The intrinsic spatial inversion asymmetry enables the generation of robust zero-bias photocurrents. Our transport simulations reveal an exceptional sensitivity to the incident polarization state, yielding a broadband optical extinction ratio of up to 10 7 . Microscopically, the inherent half-metallicity rigorously confines optical excitations to a single spin subband within the 1.2–2.5 eV photon energy range, facilitating the continuous generation of fully spin-polarized current (FSPC). Once the excitation energy exceeds the 2.5 eV threshold, simultaneous interband transitions in both spin channels are activated. At critical polarization orientations, the macroscopic charge flux undergoes exact cancellation, selectively driving a pure spin current (PSC). These mechanisms seamlessly decouple charge and spin transport, establishing the versatile MA 2 Z 4 family as a promising two-dimensional platform for low-dissipation spintronics and high-sensitivity polarimetric detection.