Probing charge density wave phases and the Mott transition in <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML"><mml:mrow><mml:mn>1</mml:mn><mml:mi>T</mml:mi></mml:mrow><mml:mo>−</mml:mo><mml:msub><mml:mrow><mml:mi>TaS</mml:mi></mml:mrow><mml:mn>2</mml:mn></mml:msub></mml:math> by inelastic light scattering
Sanja Djurdjić Mijin, Andreas Baum, J Bekaert, Andrijana Šolajić, Jelena Pešić, Yu Liu, Ge He, M. V. Miloševıć, C. Petrović, Zoran V. Popović, R. Hackl, N. Lazarević
Abstract
We present a polarization-resolved, high-resolution Raman scattering study of the three consecutive charge density wave (CDW) regimes in $1T\ensuremath{-}{\mathrm{TaS}}_{2}$ single crystals, supported by ab initio calculations. Our analysis of the spectra within the low-temperature commensurate (C-CDW) regime shows $P\overline{3}$ 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 sizable electron-phonon coupling. Between 200 and 352 K, our Raman spectra show contributions from both the IC-CDW and the C-CDW phases, 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 ${\mathrm{\ensuremath{\Omega}}}_{\mathrm{gap}}\ensuremath{\approx}170\text{--}190$ meV, and track its temperature dependence.