Ferron-driven photoferroic hysteresis in van der Waals CuInP2S6.

Controlling ferroelectric polarization with light promises a frontier for ultrafast optoelectronics. Yet the fundamental mechanism by which transient photoexcitation produces persistent photocurrent retention has remained elusive. Here we demonstrate a quasiparticle state that mediates photoferroic retention in the van der Waals ferroelectric CuInP2S6. We identify ferrons, collective excitations of dipole-carrying lattice vibrations, as carriers of optically imprinted polarization states. Narrowband resonant ferron oscillations at 2.16 THz exhibit a butterfly-shaped hysteresis that mirrors the photocurrent hysteresis response, directly linking ferron dynamics to polarization-dependent photocurrent retention at room temperature. Above-bandgap photoexcitation drives ferron formation through displacive excitation of coherent lattice motion, enabling carrier-mediated reconfiguration of ferroelectric domains, while sub-bandgap excitation leaves the polarization unaltered. The analytical calculations quantitatively capture the symmetry-dependent photocurrent generation and the consequence of the ferron-mediated hysteresis. These results establish ferronics, the manipulation of ferroelectric order through ferron quasiparticles, as a distinct paradigm for optically controlled polarization and photocurrent retention in low-dimensional quantum materials.