Unveiling the underlying interactions in Ta2NiSe5 from photo-induced lifetime change

TL;DR

This study combines theoretical simulations and TR-ARPES experiments to analyze the electronic and lattice interactions in Ta2NiSe5, revealing that electron-electron interactions primarily influence its insulating state and spectral broadening.

Contribution

It introduces a comparative analysis method that distinguishes electronic from phononic effects in photo-doped insulators, emphasizing the dominance of electron-electron interactions in Ta2NiSe5.

Findings

Electronic lifetime broadening dominates spectral changes.

Electron-electron interactions are key to the insulating state.

Bandgap renormalization depends on proximity to phase transition.

Abstract

We present a generic procedure for quantifying the interplay of electronic and lattice degrees of freedom in photo-doped insulators through a comparative analysis of theoretical many-body simulations and time- and angle-resolved photoemission spectroscopy (TR-ARPES) of the transient response of the candidate excitonic insulator Ta2NiSe5. Our analysis demonstrates that the electron-electron interactions dominate the electron-phonon ones. In particular, a detailed analysis of the TRARPES spectrum enables a clear separation of the dominant broadening (electronic lifetime) effects from the much smaller bandgap renormalization. Theoretical calculations show that the observed strong spectral broadening arises from the electronic scattering of the photo-excited particle-hole pairs and cannot be accounted for in a model in which electron-phonon interactions are dominant. We demonstrate that the magnitude of the weaker subdominant bandgap renormalization sensitively depends on the distance from the semiconductor/semimetal transition in the high-temperature state, which could explain apparent contradictions between various TR-ARPES experiments. The analysis presented here indicates that electron-electron interactions play a vital role (although not necessarily the sole one) in stabilizing the insulating state.