Terahertz Field Control of Electronic-Ferroelectric Anisotropy at Room Temperature in LuFe2⁢O4

Electronic ferroelectrics, with polarization 𝑷 induced by strongly correlated charges, are expected to show ultrafast, huge, and flexible responses required in future optoelectronics. Although the challenges for ultrafast manipulation of such a polarization are ongoing, the expected advantages have been unclear. In this Letter, we demonstrate an unprecedentedly large increase by a factor of 2.7 in optical second harmonic generation at room temperature in the prototypical electronic ferroelectrics, the rare-earth ferrite LuFe2⁢O4, by applying a terahertz field of 260  kV/cm. The transient anisotropy indicates that the direction of macroscopic polarization can be controlled three dimensionally on subpicosecond timescales, offering additional degrees of freedom in controlling polarization. Although the polarization response is in phase concerning the terahertz field, its sensitivity increased with delay, indicating that cooperative interactions among microscopic domains play an important role in the unprecedented response.