Strongly Enhanced Charge-Density Waves and Correlated Insulating State in Atomically Thin 1$T$-TaS$_2$

Abstract

We investigate thickness-dependent charge-density-wave (CDW) transitions in 1$T$-TaS$_2$ using temperature-dependent Raman spectroscopy and electrical transport. Raman measurements show that the incommensurate, nearly commensurate, and commensurate CDW phases persist down to the monolayer limit. As the thickness is reduced, the transition temperatures increase, accompanied by an orders-of-magnitude rise in sheet resistance and a sharp reduction in the carrier localization length. The first-order hysteretic CCDW-NCCDW transition is uniquely absent in the monolayer. Calculations suggest that the enhanced CDW in thin layers originates from strengthened Coulomb interactions due to reduced out-of-plane screening, particularly in the nonlocal component. These findings highlight the cooperative roles of electron correlation, electron-phonon interaction, and interlayer coupling in shaping the ground state and transition dynamics of atomically thin 1$T$-TaS$_2$, opening pathways for engineering correlated phases in two-dimensional CDW systems.