probed by time- and angle-resolved photoemission spectroscopy

The charge density wave (CDW) phase of bulk 1T-VSe₂ gives rise to only subtle spectroscopic signatures [1-2], leaving unresolved the debate about dominant interactions driving the transition [3]. Here, we optically excite this material with an intense infrared femtosecond pulse, taking it out of its equilibrium CDW state, and probe the evolution of the transient quasiparticle dispersion with time- and angle-resolved photoemission spectroscopy. By monitoring the relaxation of light-induced hot electrons, we extract the time-dependent hot carrier temperature and find that the excited electrons reach a metastable thermal equilibrium with a strongly-coupled optical phonon mode on the timescale of 200 fs. The increase in hot phonon population available to scatter with photoholes leads to an increased linewidth of quasiparticle bands across the entire valence spectrum. We elucidate the role of electron-phonon interactions on the dynamics in this system and discuss the implications of our observations for the response to strong optical excitation in related CDW systems.

[1] Jolie, et al., Phys. Rev. B 99, 115417 (2019).
[2] Strocov, et al., Phys. Rev. Lett. 109, 086401 (2012).
[3] Henke, arXiv: 1911.11112v2 (2019).