Large electric field-induced optical rotation in a ferroaxial crystal

A research team from the University of Tokyo’s School of Engineering has successfully observed a pronounced "linear electrogyration" effect, wherein an applied electric field induces optical rotation, in ferroaxial NiTiO₃.

Linear electrogyration, in which the polarization plane of light is rotated in proportion to an applied electric field, is a phenomenon found in various crystalline materials. While it offers potential for the development of fast, energy-efficient polarization control devices, the typically small magnitude of the effect has long limited its practical application. In this study, the team focused on NiTiO₃, a ferroaxial material with spontaneous rotational distortions, and discovered that at near-infrared wavelengths corresponding to specific electronic transitions of Ni²⁺ ions, the electrogyration coefficient reaches approximately 8 × 10⁻³ degrees per volt at low temperatures—comparable to the highest values previously observed in ferroelectric Pb₅Ge₃O₁₁ near its phase transition.

Furthermore, the team demonstrated that this effect can be artificially enhanced at room temperature by engineering a laminated structure of NiTiO₃ crystals. By stacking crystals with opposite ferroaxial distortions and applying an electric field alternately across the layers, they successfully doubled the optical rotation angle, with the potential for further amplification by increasing the number of layers.

These findings not only shed light on the microscopic mechanisms of electrogyration but also open new pathways toward realizing energy-efficient, high-performance polarization control devices.

Papers
Journal: Advanced Optical Materials
Title: Large Electrogyration Effect in Ferroaxial NiTiO₃ at Near Infrared Wavelengths
Authors: Takeshi Hayashida, Koei Matsumoto, and Tsuyoshi Kimura
DOI: 10.1002/adom.202500364