Hidden Quantum State and Signature of Mott Transition in 2D 1T–TaS₂

Herein, a comprehensive inelastic light scattering studies on 1T–TaS₂ with different thicknesses is reported. This compound is well‐known for its rich charge density wave phases. Along with that, it has been one of the promising candidates for a quantum spin‐liquid state as the spins reside on a triangular lattice, and it does not show any signature of magnetic ordering. A thickness‐dependent Raman measurement is performed in a regime of completely commensurate charge density wave (CDW) to a nearly commensurate CDW with varying temperature (4–330 K) and polarization direction of the incident light. This study observes the signature of CDW transition and in addition to that has found the signature of a well‐sought hidden quantum CDW state at a low temperature of around T_H ≈ 80 K. The emergence of CDW, both normal and hidden one, is marked by the emergence of new phonon modes and distinct renormalized phonon self‐energy parameters for the most prominent modes. A transition from metallic to the Mott insulating state is gauged via the Raman response using low‐frequency slope, reflected in the renormalized slope below T_CDW and T_H.