# Direct determination of mode-projected electron-phonon coupling in the time-domain

## TL;DR

This paper introduces a novel time-domain method using TR-ARPES to directly measure electron-phonon coupling strengths in quantum materials, demonstrated in graphite by analyzing electron dynamics and phonon emission.

## Contribution

A new approach for directly quantifying electron-phonon coupling in the time domain using TR-ARPES, enabling mode-specific measurements with high sensitivity.

## Key findings

- Quantized energy-loss processes observed in graphite.
- Characteristic timescale for spectral-weight transfer measured.
- Direct extraction of electron-phonon matrix elements achieved.

## Abstract

Ultrafast spectroscopies have become an important tool for elucidating the microscopic description and dynamical properties of quantum materials. In particular, by tracking the dynamics of non-thermal electrons, a material's dominant scattering processes -- and thus the many-body interactions between electrons and collective excitations -- can be revealed. Here we present a new method for extracting the electron-phonon coupling strength in the time domain, by means of time and angle-resolved photoemission spectroscopy (TR-ARPES). This method is demonstrated in graphite, where we investigate the dynamics of photo-injected electrons at the K point, detecting quantized energy-loss processes that correspond to the emission of strongly-coupled optical phonons. We show that the observed characteristic timescale for spectral-weight-transfer mediated by phonon-scattering processes allows for the direct quantitative extraction of electron-phonon matrix elements, for specific modes, and with unprecedented sensitivity.