Multimode vibrational coupling across the insulator-to-metal transition in 1T-TaS2 in THz cavities.

The use of optical cavities on resonance with material excitations allows controlling light–matter interaction in both the regimes of weak and strong coupling. We study here the multimode vibrational coupling of low energy phonons in the charge-density-wave material 1T-TaS₂ across its insulator-to-metal phase transition. For this purpose, we embed 1T-TaS₂ into THz Fabry–Pérot cryogenic cavities tunable in frequency within the spectral range of the vibrational modes of the insulating phase and track the linear response of the coupled phonons across the insulator-to-metal transition. In the low temperature dielectric state, we reveal the signatures of a multimode vibrational strong collective coupling. The observed polariton modes inherit character from all the vibrational resonances as a consequence of the cavity-mediated hybridization. We reveal that the vibrational strong collective coupling is suppressed across the insulator-to-metal transition as a consequence of the phonon-screening induced by the free charges. Our findings emphasize how the response of cavity-coupled vibrations can be modified by the presence of free charges, uncovering a new direction toward the tuning of coherent light–matter interaction in cavity-confined correlated materials. [ABSTRACT FROM AUTHOR]