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.