# Reassessing Graphene Absorption and Emission Spectroscopy

## TL;DR

This paper reinterprets graphene's optical absorption and emission spectra, emphasizing the significance of phonon-assisted indirect processes over direct transitions, challenging previous ultrafast relaxation assumptions.

## Contribution

It introduces a new framework highlighting the role of phonon-assisted processes in graphene spectroscopy, replacing the need for ultrafast relaxation explanations.

## Key findings

- Indirect processes explain UV excess absorption.
- Fast emission is dominated by phonon-assisted processes.
- No ultrafast relaxation needed to match spectra.

## Abstract

We present a new paradigm for understanding optical absorption and hot electron dynamics experiments in graphene. Our analysis pivots on assigning proper importance to phonon assisted indirect processes and bleaching of direct processes. We show indirect processes figure in the excess absorption in the UV region. Experiments which were thought to indicate ultrafast relaxation of electrons and holes, reaching a thermal distribution from an extremely non-thermal one in under 5-10 fs, instead are explained by the nascent electron and hole distributions produced by indirect transitions. These need no relaxation or ad-hoc energy removal to agree with the observed emission spectra and fast pulsed absorption spectra. The fast emission following pulsed absorption is dominated by phonon assisted processes, which vastly outnumber direct ones and are always available, connecting any electron with any hole any time. Calculations are given, including explicitly calculating the magnitude of indirect processes, supporting these views.