Hidden Quantum State and Signature of Mott Transition in Two-dimensional 1T-TaS2

TL;DR

This study uses inelastic light scattering to investigate charge density wave phases and a hidden quantum state in 1T-TaS2, revealing a transition to a Mott insulator and identifying a hidden quantum CDW at low temperature.

Contribution

It provides the first comprehensive Raman analysis of thickness-dependent CDW transitions and uncovers a hidden quantum CDW state in 1T-TaS2.

Findings

Detection of CDW transition signatures via phonon mode changes

Identification of a hidden quantum CDW state around 80K

Observation of a transition from metallic to Mott insulating state

Abstract

Here we report a comprehensive inelastic light scattering studies on 1T-TaS2 with different thickness. 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. We performed a thickness dependent Raman measurement in a regime of completely commensurate charge density wave (C-CDW) to a nearly commensurate charge density wave (NC-CDW) with varying temperature (4K-330K) and polarization direction of the incident light. We observed the signature of CDW transition and in addition to that we have also found the signature of a well sought hidden quantum CDW state at low temperature around TH ~ 80K. 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 TCDW and TH.