Magnetoelectric Raman Force on Shear Phonons in a Frustrated van der Waals Bilayer Magnet

TL;DR

This paper demonstrates how coherent phonon generation via second order response to electric laser fields can be extended to frustrated quantum magnets, specifically analyzing the Raman force on shear phonons in a bilayer magnet with complex magnetic order.

Contribution

It introduces a theoretical framework for understanding the Raman force on shear phonons in a frustrated magnetoelectric bilayer, incorporating magnon-phonon coupling and anisotropic responses.

Findings

Raman force is highly anisotropic.

Raman force sensitivity depends on magnon lifetime.

Magnon-phonon interactions are significant in frustrated bilayer magnets.

Abstract

We show that the concept of coherent phonon generation by second order response to incident electric laser fields, which is a hallmark of pump-probe spectroscopy on conventional solids, can be expanded to include frustrated quantum magnets. For that purpose, we analyze the Raman force on the shear phonons of a frustrated magnetoelectric bilayer spin system. The bilayer is a stacked triangular magnet, motivated by recently emerging type-II van der Waals multiferroic transition metal dihalides and comprises a spin system which allows for incommensurate spiral order. The magnon excitations are treated by linear spin wave theory. In the spiral state, a finite electric polarization is obtained from the spin-current interaction which induces a coupling of the magnons to the electric field. Scattering of the bilayer shear phonons from the magnons is derived from a magnetoelastic energy. In this scenario, a mixed three-point response function for the Raman force is evaluated. We find it to be strongly anisotropic and very sensitive to the magnon lifetime.