First-Principles Exciton-Phonon and Magnon-Phonon Interactions: Theory, Code, Applications, and New Directions

Electron-phonon (e-ph) interactions have become a major focus of first-principles electronic structure calculations. Taking these methods in a new direction, recent work has shown accurate predictions of exciton-phonon interactions by combining first-principles e-ph and Bethe-Salpeter equation calculations [1].

In this talk, I will briefly review the theory and code for first-principles exciton-phonon calculations, and show application of this formalism to study exciton nonradiative processes, light-matter interaction, and ultrafast exciton dynamics, including predictions of time-domain spectroscopies [1,2].

I will then discuss the addition of the spin degree of freedom to this framework, which enables calculations of magnon-phonon interactions and the associated magnon dynamics [3]. I will show results for two-dimensional ferromagnetic semiconductors, where our method can predict magnon mean free paths and identify phonon modes strongly coupled to magnons, providing useful microscopic insights for applications in spintronics and spin-based quantum technologies.

To conclude, I will highlight new frontiers of this research, including combined time-domain exciton and phonon dynamics, compressing exciton-phonon interactions, and methods to address strongly coupled excitons and phonons. Advances in the Perturbo code [4] enabling these calculations will also be discussed.