Direct observation of melted Mott state evidenced from Raman scattering in 1T-TaS2 single crystal*

The evolution of electron correlation and charge density wave (CDW) in 1T-TaS2 single crystal has been investigated by temperature-dependent Raman scattering, which undergoes two obvious peaks of A 1g modes about 70.8 cm−1 and 78.7 cm−1 at 80 K, respectively. The former peak at 70.8 cm−1 is accordant with the lower Hubbard band, resulting in the electron-correlation-driven Mott transition. Strikingly, the latter peak at 78.7 cm−1 shifts toward low energy with increasing the temperature, demonstrating the occurrence of nearly commensurate CDW phase (melted Mott phase). In this case, phonon transmission could be strongly coupled to commensurate CDW lattice via Coulomb interaction, which likely induces appearance of hexagonal domains suspended in an interdomain phase, composing the melted Mott phase characterized by a shallow electron pocket. Combining electronic structure, atomic structure, transport properties with Raman scattering, these findings provide a novel dimension in understanding the relationship between electronic correlation, charge order, and phonon dynamics.