We present a polarization-resolved, high-resolution Raman scattering study of the three consecutive charge density wave (CDW) regimes in 1T-TaS2 single crystals, supported by \textit{ab initio} calculations. Our analysis of the spectra within the low-temperature commensurate (C-CDW) regime shows P3 symmetry of the system, thus excluding the previously proposed triclinic stacking of the "star-of-David" structure, and promoting trigonal or hexagonal stacking instead. The spectra of the high-temperature incommensurate (IC-CDW) phase directly project the phonon density of states due to the breaking of the translational invariance, supplemented by sizeable electron-phonon coupling. Between 200 and 352\,K, our Raman spectra show contributions from both the IC-CDW and the C-CDW phase, indicating their coexistence in the so-called nearly-commensurate (NC-CDW) phase. The temperature-dependence of the symmetry-resolved Raman conductivity indicates the stepwise reduction of the density of states in the CDW phases, followed by a Mott transition within the C-CDW phase. We determine the size of the Mott gap to be Ωgap≈170−190 meV, and track its temperature dependence.
@article{arxiv.2102.04821,
title = {Probing charge density wave phases and the Mott transition in $1T$-TaS$_2$ by inelastic light scattering},
author = {S. Đurđić Mijin and A. Baum and J. Bekaert and A. Šolajić and J. Pešić and Y. Liu and Ge He and M. V. Milošević and C. Petrovic and Z. V. Popović and R. Hackl and N. Lazarević},
journal= {arXiv preprint arXiv:2102.04821},
year = {2021}
}