Abstract

The problem of exciton-phonon interaction in crystals concerns the simultaneous description of the interaction of excited electron-hole pairs both with themselves and with lattice vibrations. It has become increasingly relevant to both experimental and theoretical research. It is invoked, for example, to explain fine structures in optical absorption and luminescence spectra of low-dimensional semiconductors, to model the width of excitonic spectral peaks, and to explain the out-of-equilibrium carrier dynamics in ultrafast spectroscopy in terms of lifetimes and intervalley scatterings. I will first briefly introduce the concepts of phonons and excitons from a many-body point of view and in the context of ab initio, first-principles simulations. Then, starting from the static Bethe-Salpeter equation (BSE) – which is the state-of-the-art tool to compute excitons – I will present the theoretical approach to obtain spectroscopic observables including a microscopic description of exciton-phonon interactions, with a particular focus on the role of electronic screening. I will then discuss the computational implementation of a workflow for efficient exciton-phonon calculations – as recently implemented in the Yambo code – obtained by exploiting symmetry operations on exciton wavefunctions and electron-phonon matrix elements in momentum space. Finally, I will illustrate applications of this methodology for the characterization of relevant layered and 2D materials, including phonon-assisted satellites appearing in the luminescence spectra of boron nitride, as well as scattering amplitudes and Raman spectra in monolayer transition metal dichalcogenides.