Magnetic order induced polarization anomaly of Raman scattering in 2D magnet CrI$_3$

TL;DR

This study reveals that magnetic ordering in 2D CrI3 significantly alters Raman polarization selection rules, demonstrating a strong spin-phonon coupling effect that influences optical phonon behavior in monolayer and bilayer samples.

Contribution

It uncovers how magnetic order modifies Raman selection rules in 2D CrI3, highlighting a novel magneto-optical effect linked to spin-phonon interactions.

Findings

Enhanced A1g peak intensity in cross polarization at low temperature for monolayer

Absence of the peak in bilayer AFM state, reappearing in FM state under magnetic field

Magnetic order influences Raman polarization selection rules in 2D CrI3

Abstract

The recent discovery of 2D magnets has revealed various intriguing phenomena due to the coupling between spin and other degree of freedoms (such as helical photoluminescence, nonreciprocal SHG). Previous research on the spin-phonon coupling effect mainly focuses on the renormalization of phonon frequency. Here we demonstrate that the Raman polarization selection rules of optical phonons can be greatly modified by the magnetic ordering in 2D magnet CrI$_3$. For monolayer samples, the dominant A$\rm_{1g}$ peak shows abnormally high intensity in the cross polarization channel at low temperature, which is forbidden by the selection rule based on the lattice symmetry. While for bilayer, this peak is absent in the cross polarization channel for the layered antiferromagnetic (AFM) state and reappears when it is tuned to the ferromagnetic (FM) state by an external magnetic field. Our findings shed light on exploring the emergent magneto-optical effects in 2D magnets.