# Theory of exciton dynamics in time-resolved ARPES: intra- and intervalley scattering in two-dimensional semiconductors

## TL;DR

This paper develops a microscopic theory for exciton dynamics in time-resolved ARPES, showing it can detect ultrafast exciton formation and relaxation in two-dimensional semiconductors like TMDCs.

## Contribution

It introduces a novel microscopic model for exciton dynamics in trARPES, focusing on phonon-mediated thermalization and intra- and intervalley scattering in 2D semiconductors.

## Key findings

- trARPES can probe ultrafast exciton formation and relaxation
- The theory captures phonon-mediated thermalization processes
- Excitons can be detected throughout the Brillouin zone

## Abstract

Time- and angle-resolved photoemission spectroscopy (trARPES) is a powerful spectroscopic method to measure the ultrafast electron dynamics directly in momentum-space. However, band gap materials with exceptional strong Coulomb interaction such as monolayer transition metal dichlacogenides (TMDC) exhibit tightly bound excitons, which dominate their optical properties. This rises the question whether excitons, in particular their formation and relaxation dynamics, can be detected in photoemission. Here, we develope a fully microscopic theory of the temporal dynamics of excitonic time- and angle resolved photoemission with particular focus on the phonon-mediated thermalization of optically excited excitons to momentum-forbidden dark exciton states. We find that trARPES is able to probe the ultrafast exciton formation and relaxation throughout the Brillouin zone.