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arXiv · 2102.04821

Probing charge density wave phases and the Mott transition in $1T$-TaS$_2$ by inelastic light scattering

S. Đurđić Mijin·A. Baum·J. Bekaert·A. Šolajić·J. Pešić·Y. Liu·Ge He·M. V. Milošević·C. Petrovic·Z. V. Popović·R. Hackl·N. Lazarević
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Abstract

We present a polarization-resolved, high-resolution Raman scattering study of the three consecutive charge density wave (CDW) regimes in $1T$-TaS$_2$ single crystals, supported by \textit{ab initio} calculations. Our analysis of the spectra within the low-temperature commensurate (C-CDW) regime shows $\mathrm{P3}$ 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 $\Omega_{\rm gap}\approx 170-190$ meV, and track its temperature dependence.

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S. Đurđić Mijin, A. Baum, J. Bekaert, A. Šolajić, J. Pešić, Y. Liu, Ge He, M. V. Milošević, C. Petrovic, Z. V. Popović, R. Hackl, N. Lazarević. 2021-02-09. Probing charge density wave phases and the Mott transition in $1T$-TaS$_2$ by inelastic light scattering. https://doi.org/10.1103/physrevb.103.245133

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