Ultrafast photocurrent hysteresis in photoferroelectric α-In₂Se₃ diagnosed by terahertz emission spectroscopy

Nonvolatile control over the physical state of polar materials through all-optical methods has been a long-standing objective pursued in optoelectronics. Photoferroelectric semiconductors exhibit immense potential in capturing multimodal nonvolatile states, attributed to their spontaneous and reversible in-plane and out-of-plane polarizations. Herein, we uncover an unprecedented nonvolatile, zero-bias, ultrafast photocurrent hysteresis response with an innovative all-optical approach, discerned by analyzing in-plane and out-of-plane terahertz (THz) waves emitted from photoferroelectric α-In₂Se₃. The mechanism underlying such ultrafast photocurrent hysteresis arises from anomalous linear and circular photovoltaic effects synchronously fueled by a localized rearrangement of polarization. By harnessing the anisotropic photoferroelectric kinetics-induced relative phase between the in-plane and out-of-plane polarizations, we further demonstrate the flexible selection of chirality, tunable rotational angle, and optimizable ellipticity of THz waves. Our findings present a unique ultrafast and nondestructive strategy for investigating photoferroelectric hysteresis, empowering dynamic polarization manipulation of THz waves for a wide range of THz applications.