Exciton-Exciton Annihilation Mediated by Many-Body Coulomb and Phonon Interactions: An Ab Initio Study

TL;DR

This paper develops a first-principles computational framework to analyze exciton-exciton annihilation in 2D materials, revealing picosecond-scale non-radiative decay channels mediated by Coulomb and phonon interactions.

Contribution

It introduces a novel ab initio method combining GW and Bethe-Salpeter Equation formalisms to explicitly compute EEA mechanisms and rates in excitonic materials.

Findings

Picosecond-scale exciton annihilation observed in monolayer WSe2.

Identification of scattering channels involving free electron-hole pairs.

Insights into non-radiative relaxation pathways in 2D semiconductors.

Abstract

Exciton-exciton annihilation (EEA), in which two excitons interact to generate high-energy excitations, is an important non-radiative channel in light-induced excited-state relaxation. When efficient, this process offers an alternative route to exciton emission, potentially allowing extended energetically excited particles' lifetime and coherence. These properties are significant in designing and understanding materials-based quantum devices, particularly for low-dimensional semiconductors. Here, we present a first-principles framework to compute EEA mechanisms and rates using many-body perturbation theory within the GW and Bethe-Salpeter Equation (GW-BSE) formalism. Our method explicitly accounts for Coulomb-driven and phonon-assisted exciton-exciton scattering by explicitly evaluating the interaction channels between the constituent electrons and holes composing the BSE excitons. We apply this framework to monolayer WSe$_2$ and explore the $A$, $B$ excitation manifolds, finding picosecond-scale annihilation between bright and dark states, cross valleys, and cross peak manifolds. These channels become allowed due to scattering into free electron-hole pairs across the Brillouin zone. Our results supply new insights into non-radiative exciton relaxation mechanisms in two-dimensional materials, providing a predictive and general tool for modeling these interactions in excitonic materials.