Condensed Matter Physics Seminar: Marina Filip

Abstract:

Excitons are correlated electron-hole pairs that form in semiconductors and insulators upon photoexcitation. Understanding the physics of how they form, delocalize and dissociate is of key importance to the functionality of a wide range of applications, including, but not limited to photovoltaics, lighting and lasing. First principles computational modeling techniques based on density functional theory (DFT) and many body perturbation theory are continuously developed to address complex light-matter interaction problems involving excitons and other composite quasiparticles. The GW+Bethe-Salpeter Equation (BSE) approach [1,2] is the state-of-the-art technique to compute optical excitation energies in semiconductors and insulators and understand excitons, and standard implementations currently employ the frozen ion approximation.

In the first part of my talk, I will present our studies of exciton delocalization in several heterogeneous semiconductors belonging to the broader family of halide perovskites. I will discuss our recent analysis of optical excitations in quasi-2D organic-inorganic halide perovskites [3-5], and show how subtle structural features can significantly impact the delocalization of excitons in these systems. In the second part of my talk I will present a new methodological development that generalizes the BSE to include the impact of ionic vibrations on the dielectric screening of excitons [6,7], and show how this allows us to compute the rate of dissociation of an exciton upon scattering with phonons.

1. Hybertsen & Louie, Phys. Rev. B 34, 5390 (1986).
2. Rohlfing & Louie, Phys. Rev. Lett. 81, 2312 (1998).
3. Filip, Qiu, Del Ben & Neaton, Nano Lett. 22 (12), 4870-4878 (2022).
4. McArthur, Filip & Qiu, Nano Lett. 23 (9), 3796-3802 (2023).
5. Chen & Filip, submitted (2023).
6. Filip, Haber & Neaton, Phys. Rev. Lett. 127, 67401 (2021).
7. Alvertis, Haber, Li, Coveney, Louie, Filip & Neaton, submitted (2023).