Boosting Terahertz Emission via Ultrathin Cu‐Engineered Interfacial Orbital Hybridization

Orbital angular momentum provides a promising route for developing spintronic terahertz emitters beyond conventional spin‐based mechanisms. However, efficient orbital‐to‐charge conversion and its underlying physics remain largely unexplored. Here, we report a pronounced enhancement of THz emission through interfacial orbital hybridization engineering in Cu/Pt/Co heterostructures. By inserting an ultrathin Cu layer at the Pt/SiO 2 interface, the THz emission amplitude is maximum enhanced by a factor of ∼ 361% compared with the Pt/Co/SiO 2 structure, with the maximum enhancement occurring at a Cu thickness of only 0.5 nm, followed by a rapid suppression at larger Cu thicknesses. Time‐resolved measurements combined with theoretical analysis indicate that angular momentum transport in Pt is predominantly governed by orbital currents, which gradually evolve from ballistic‐like to diffusive transport during propagation. The enhancement factor decreases progressively with increasing Pt thickness, suggesting that the enhanced conversion is mainly interfacial in origin. The XPS results, together with the interface‐isolated oxidation design, further confirm the regulatory role of the ultrathin Cu layer in interfacial oxidation‐induced orbital hybridization. These results demonstrate that oxygen‐assisted interfacial orbital hybridization can effectively enhance the inverse orbital Rashba‐Edelstein effect, providing an effective strategy for boosting THz emission through orbital engineering.