The coexistence of strong electron-phonon coupling, non-trivial topology and strong electronic
correlations in quantum materials can lead to new exciting phenomena, and the study of their interplay constitutes a new paradigm in condensed matter. Here, by means of time and angle-resolved photoemission spectroscopy (TR-ARPES) and broadband time-resolved optical spectroscopy (TROS), we investigate the effect of an optical excitation on the electronic and structural properties of two strongly coupled charge-density-wave (CDW) systems: ScV6Sn6 and VTe2. In the kagome compound ScV6Sn6, by performing TR-OS experiments, we show that the electronic subsystem is resilient to an optical perturbation up to a high excitation fluence, suggesting a major role played by the lattice in the stabilization of the low-temperature CDW phase [1]. In support of this hypothesis, the CDW in ScV6Sn6 has proved to be sensitive to a direct mechanical lattice perturbation. In particular, by applying a tensile strain to the material, we show the possibility to manipulate the frequency of the amplitude mode (AM) that characterizes the CDW phase [2]. In the TMDC compound VTe2, by using TR-OS, we unveil the presence of two independent amplitude modes of the CDW phase [3]. Moreover, by performing TR-ARPES experiments, we show that at high excitation fluences the closure of the electronic gap is not controlled by the excitation of the two CDW amplitude modes, but it takes place on a slower time scale. This timescale suggests that the gap dynamics is mostly governed by the incoherent excitation of high frequency strongly coupled optical phonons, which results in a loss of long-range order of the CDW phase [4]. The systems here considered, in which the physics of the CDW transition is markedly different from the conventional Peierls picture, provide a rich playground for studying the possibility to control these fascinating states of matter.

References
[1] Tuniz, M. et al. Commun. Mater. 4, 103 (2023).
[2] Tuniz, M. et al. arXiv:2403.18046 (2024).
[3] Tuniz, M. et al. Phys. Rev. Research 5, 043276 (2023).
[4] Tuniz, M. et al. To be submitted (2024).