Generation and Control of Ultrafast Circular Photon Drag Current in Multilayer PtSe2 Revealed Via Terahertz Emission

Abstract The generation and control of ultrafast photocurrents on the surface of transition‐metal dichalcogenides (TMDs) are essential for the development of advanced optoelectronic devices. A detailed understanding of the mechanism of ultrafast photocurrent generation is primarily needed to design functional devices. Here, it is reported that ultrafast photocurrents in multilayer PtSe 2 are induced by the photon drag effect with high conversion efficiency. Particularly, under circularly polarized laser excitation, anisotropic in‐plane photon drag currents are generated, leading to the elliptically polarized terahertz (THz) radiation directly controlled by the helicity of the pump beam. Furthermore, a new model called “THz emission by the circular ac Hall effect” (TECacHE) is proposed to unveil the carrier transport process. It is observed that the origins of elliptically polarized THz emission controlled by helicity involve the pure circular photon drag current and the retardation induced by the Lorentz force. Besides, ultrafast ternary encoding is proposed and demonstrated by polarized THz emission. The results not only provide a new contactless detection model to study surface ultrafast photocurrents but also afford a fundamental investigation of the circular photon drag current in layered TMDs for THz telecommunication devices.