Raman Optical Activity Induced by Ferroaxial Order in NiTiO$_3$

TL;DR

This study demonstrates that Raman optical activity can originate from ferroaxial order in centrosymmetric NiTiO$_3$, expanding the understanding of ROA beyond chiral molecules and magnetic materials.

Contribution

It reveals that ROA can be induced by ferroaxial order in centrosymmetric, non-magnetic crystals, supported by experimental and theoretical analysis.

Findings

Pronounced ROA signal observed in NiTiO$_3$ correlates with ferroaxial domains.

Symmetry analysis and calculations show ROA originates from ferroaxial order.

ROA can serve as a probe for ferroaxial order in centrosymmetric systems.

Abstract

Raman optical activity (ROA), the dependence of Raman intensity on the circular polarization of incident and scattered light, has traditionally been observed in chiral molecules and magnetic materials, where inversion or time-reversal symmetry is broken. Here we demonstrate that ROA can also arise in a centrosymmetric and non-magnetic ferroaxial crystal. Using circularly polarized Raman spectroscopy on single-crystalline NiTiO$_3$, we observed a pronounced ROA signal in the cross-circular polarization configurations, which correlates with the ferroaxial domain structure. Our symmetry analysis, first-principles calculations of phonons, and tight-binding model calculations reveal that the natural ROA originates from the ferroaxial order and persists even within the electric dipole approximation. These results establish ROA as a powerful probe of ferroaxial order in centrosymmetric systems.