Electromagnons in CrI₃ from nonadiabatic DFPT at constrained magnetic moments

The terahertz dynamics of CrI₃, a prototypical van der Waals insulating ferromagnet stable down to the monolayer limit, has garnered significant interest due to the potential for externally manipulating spin-wave excitations (magnons),[1,2] thus opening avenues for low-power computing technologies. The rich magnonic behavior in CrI₃ stems from a complex interplay between spin, lattice, and electronic degrees of freedom, which remains challenging to fully understand at the microscopic level. [3,4] In this talk, I will present a first-principles investigation of these interactions using a nonadiabatic extension of the density-functional perturbation theory (DFPT) formulated at constrained magnetic moments. By computing frequency-dependent susceptibilities (magnetic, dielectric, and magnetoelectric) with and without spin and ionic relaxation effects, we uncover a key coupling between an optical electromagnon and a nearby polar phonon mode. This coupling leads to a pronounced lattice-mediated local magnetoelectric response and the emergence of electromagnon signatures in the dielectric spectrum, including notable magnetic circular dichroism.

[1] L. Chen et al., Phys. Rev. X 8, 041028 (2018).

[2] J. Cenker et al., Nat. Phys. 17, 20 (2021).

[3] P. Delugas et al., Phys. Rev. B 107, 214452 (2023).

[4] S. Ren et al., Phys. Rev. X 14, 011041 (2024).