Enhanced Terahertz Emission Enabled by Circular Photogalvanic Effect.

Topological materials host exotic phenomena rooted in their distinctive band topology, where band splitting plays a central role in spin transport and nonlinear optical responses. Terahertz (THz) emission spectroscopy provides a time-resolved probe of carrier dynamics governed by band splitting. In ferromagnet-topological material heterostructures, THz emission is typically attributed to spin-to-charge conversion (SCC). However, emerging experimental observations indicate that the SCC mechanism alone cannot fully account for the dominant origin of THz emission in certain systems, the potential contribution of band splitting in topological materials remaining unexplored. Here, we demonstrate that PtTe_{2}/Cr_{5}Te_{6} heterostructures exhibit enhanced, field-free THz emission that is not driven by SCC, but by the circular photogalvanic effect (CPGE). Supported by the control experiments and first-principles calculations, we show that band engineering at the heterointerface is essential for CPGE-driven ultrafast photocurrents. Remarkably, the polarity of the emitted THz wave can be reversibly and deterministically switched by the laser helicity without altering the magnetic field. These findings highlight the photogalvanic effect as a powerful and versatile origin of THz generation in spintronic heterostructures. Our Letter paves a pathway toward all-optical, helicity-controlled ultrafast THz sources and spin-optoelectronic devices based on quantum materials.