Coherent phonons and the interplay between charge density wave and Mott phases in 1<i>T</i>-TaSe₂

1T-TaSe₂ is an ideal system in which to explore the phenomenon of coexisting order since it is host to both a charge density wave (CDW) and Mott phase at low temperature. We investigated the CDW-Mott phase in 1T-TaSe₂ at 77 K using a combination of time- and angle-resolved photoemission spectroscopy (TR-ARPES) and time-resolved reflectivity (TRR) which reveals strong coherent phonon oscillations [1]. Most importantly, we find that perturbation using a femtosecond laser pulse in TR-ARPES triggers a modulation of the Mott gap with a single frequency related to the in-plane CDW amplitude mode, whereas TRR measurements show a modulation comprised of multiple frequencies belonging to the distorted CDW lattice modes. Our results clearly identify the relationship of the in-plane CDW amplitude mode with the Mott phase in 1T-TaSe₂ and highlight the importance of lattice degrees of freedom.

[1] C. J. Sayers et al. Phys. Rev. B. 102, 161105(R) (2020)