Capturing exciton interactions, dephasing, and Floquet-like physics from first principles

In the last two decades, first-principles methods based on many-body perturbation theory and interacting Green’s function, such as the Bethe-Salpeter equation, have allowed for the unbiased and accurate description of optical properties of materials. Yet, despite the progress in such methods, they are typically applicable only for the description of single excitons composed of an individual, interacting electron-hole pair. Here, we present recently developed formalisms for computing the interaction of excitons with other quasiparticles and collective excitations from first principles.



We will present recently developed formalisms for computing exciton-phonon and exciton-exciton interactions from first-principles calculations on low-dimensional materials. We compute exciton linewidth on monolayer MoS₂, where we show that coherent interactions between phonons and photons yield a factor of three increase of the exciton linewidth compared to the typically considered, first-order process. We will discuss nonlinearities predicted in the optical properties of monolayer materials, and how we can understand them within the language of an exciton-driven Bloch-Floquet effect. Finally, we will comment on how stochastic techniques can be easily incorporated into standard many-body-based codes, allowing one to study structurally complex materials directly with MBPT-based methods.