Ultrafast Anisotropic Polarization Dynamics of Electronic Ferroelectrics LuFe2O4

TL;DR

This study uses femtosecond laser pulses and second harmonic generation to reveal ultrafast, anisotropic polarization dynamics in LuFe2O4, demonstrating control of electronic ferroelectricity on femtosecond timescales.

Contribution

It provides the first direct observation of anisotropic polarization changes in LuFe2O4 induced by ultrafast photoexcitation, revealing a hidden photoexcited state affecting charge ordering.

Findings

In-plane SHG decreases immediately after excitation.

Inter-plane SHG increases, indicating polarization enhancement along c-axis.

Electronic ferroelectricity can be manipulated on femtosecond timescales.

Abstract

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 inter-plane (c-axis) SHG increased. This means that a hidden photoexcited state, in which the in-plane charge ordering is broken but the polarization along c-axis direction enhanced, has been created by photoexcitation, indicating that the electronic ferroelectricity can be controlled on a femtosecond scale.