Ferroelectric materials possess spontaneous polarization states that can be switched between two stable minima, making them attractive for non-volatile memory applications. Conventionally, polarization switching has been driven by electrical fields, but the nanosecond timescales of alternating currents only allow access to the final switched state. With the advent of ultrafast laser techniques, it has become possible to probe nonequilibrium dynamics, and light-driven ferroelectric switching has been explored in perovskites due to their low coercive fields. However, achieving sub-picosecond switching in conventional ferroelectrics remains challenging because of strong depolarization fields and domain interactions.
Recently, hafnia-based ferroelectrics have emerged as promising candidates for ultrafast switching, owing to their weak domain–domain interactions and unique phonon band structure. In this talk, I will present the first realization of sub-picosecond ferroelectric polarization switching in Hf0.5Zr0.5O2 films integrated with terahertz (THz) nanoresonators. By exploiting single-cycle THz pulses that provide enhanced local fields up to 8 MV/cm, we demonstrate collinear polarization switching with femtosecond resolution. The measurements reveal an S-shaped hysteresis capturing the negative capacitance, as well as a pronounced wake-up effect after irradiation with more than 108 THz pulses. These results establish hafnia ferroelectrics as a viable platform for light-driven ultrafast electronics and energy-efficient memory technologies.