Analysis methodology of coherent oscillations in time- and angle-resolved photoemission spectroscopy

TL;DR

This paper introduces a frequency domain analysis method for time- and angle-resolved photoemission spectroscopy data, enabling detailed study of coherent phonon-induced electronic oscillations in complex quantum materials.

Contribution

It presents a novel approach using frequency domain representation of trARPES data to analyze multiple phonon modes and electronic bands, addressing challenges from complex spectral shapes and correlations.

Findings

Frequency domain analysis distinguishes energy, linewidth, and intensity oscillations.

Composite spectra visualize phonon effects on electronic bands.

Linearly chirped pulses can introduce artifacts, separable from genuine signals.

Abstract

Oscillatory signals from coherently excited phonons are regularly observed in ultrafast pump-probe experiments on condensed matter samples. Electron-phonon coupling implies that coherent phonons also modulate the electronic band structure. These oscillations can be probed with energy and momentum resolution using time- and angle-resolved photoemission spectroscopy (trARPES) which reveals the orbital dependence of the electron-phonon coupling for a specific phonon mode. However, a comprehensive analysis remains challenging when multiple coherent phonon modes couple to multiple electronic bands. Complex spectral line shapes due to strong correlations in quantum materials add to this challenge. In this work, we examine how the frequency domain representation of trARPES data facilitates a quantitative analysis of coherent oscillations of the electronic bands. We investigate the frequency domain representation of the photoemission intensity and \tred{the first moment of the energy distribution curves}. Both quantities provide complimentary information and are able to distinguish oscillations of binding energy, linewidth and intensity.We analyze a representative trARPES dataset of the transition metal dichalcogenide WTe$_2$ and construct composite spectra which intuitively illustrate how much each electronic band is affected by a specific phonon mode. We also show how a linearly chirped probe pulse can generate extrinsic artifacts that are distinct from the intrinsic coherent phonon signal.