Ultrafast anisotropic polarization dynamics of electronic ferroelectric LuFe2O4

Femtosecond time-resolved second-harmonic generation (SHG) measurements were performed at room temperature on a single crystal of LuFe₂O₄, which has recently attracted attention as an electronic ferroelectric material in which polarization occurs due to the real-space arrangement of Fe²⁺ and Fe³⁺. We irradiated the crystal with 800-nm laser pulses, traced the subsequent SHG changes, and observed anisotropic polarization dynamics: immediately after photoexcitation, the in-plane ($ab$-plane) component of the SHG greatly reduced, while the interplane (c axis) SHG increased. This means that a hidden photoexcited state, in which the in-plane charge ordering is broken but the polarization along the c-axis direction enhanced, has been created by photoexcitation, indicating that the electronic ferroelectricity can be controlled on a femtosecond scale.