Enhanced Terahertz Emission via Synergistic Spin-Orbit Conversion in CoPt/Pt/W Multilayers

Terahertz (THz) emitters based on spin-to-charge conversion have become a key focus in spintronics. While the orbital degree of freedom enables longer-range ballistic transport in some specific material systems and offers new opportunities for high-density information devices, synergistic THz enhancement mechanisms integrating multiple quantum states and advanced interfacial engineering remain largely unexplored. Here, a “spin–orbit dual–engine” mechanism is proposed that breaks the traditional single-degree-of-freedom paradigm. Through precise design of CoPt/Pt/W heterointerfaces, spatiotemporally synchronized conversion between spin and orbital currents is achieved. Upon femtosecond laser excitation, the CoPt alloy simultaneously generates both spin and orbital polarizations. The spin current is converted into a transverse charge current via the inverse spin Hall effect in Pt, while the orbital current propagates ballistically through W and induces charge accumulation via the interfacial inverse orbital Rashba–Edelstein effect. Compared with the CoPt/Pt bilayer, which shows ≈140% higher THz emission than the conventional Co/Pt structure, the CoPt/Pt/W trilayer delivers an additional ≈138% enhancement over CoPt/Pt, demonstrating clear superiority for high-efficiency THz sources. This work establishes a universal framework for multi-quantum-state synergy, advancing the design of coupled spin–orbit systems to overcome efficiency bottlenecks in THz sources.