Theoretical Study on the Raman Effect Due to Magnons in Two-Dimensional Magnets

Raman spectroscopy is one of the most useful experimentaltoolsfor studying elementary excitations in two-dimensional (2D) materials.The Raman scattering due to phonons was widely employed for detectingstructural evolutions, especially those caused by magnetic phase transitionsin 2D magnets. A first-principles theory of the Raman scattering effectcaused by magnons is still lacking. We theoretically study the magnonRaman effect in 2D magnet CrI3. We propose a first-principlesmethod and have calculated the intensity of circularly polarized Ramansignals due to different magnon modes in the CrI3 monolayerand bilayers. The calculated Raman intensities due to magnons in theCrI(3) monolayer and the rhombohedral bilayer are consistentwith the selection rule deduced from the magnon pseudoangular momentand the parity of magnon modes. We also find that the selection ruleis violated in the symmetry-broken monoclinic bilayer due to interlayercoupling.

Automated summary

Raman spectroscopy is a valuable tool for studying elementary excitations in 2D materials. This study focuses on the magnon Raman effect in the 2D magnet CrI3. A first-principles method is proposed and used to calculate the Raman intensities due to different magnon modes in CrI3 monolayers and bilayers. The results show that the selection rule deduced from magnon pseudoangular moment and magnon mode parity holds for CrI3 monolayers and rhombohedral bilayers, but is violated in the symmetry-broken monoclinic bilayers due to interlayer coupling.