Robust charge-density wave strengthened by electron correlations in monolayer 1T-TaSe2 and 1T-NbSe2

TL;DR

This paper demonstrates a monolayer 1T-TaSe2 exhibits a robust charge-density wave and Mott-insulating phase with a transition temperature around 530 K, significantly higher than bulk, due to enhanced electron correlations and lattice effects.

Contribution

It reports the discovery of a high-temperature 2D CDW-Mott phase in monolayer 1T-TaSe2, showing enhanced electron correlations and stability over bulk materials.

Findings

Transition temperature of CDW-Mott phase ~530 K in monolayer 1T-TaSe2

Survival of lower Hubbard band under doping and photoexcitation

Enhanced Mott-Hubbard and CDW gaps compared to NbSe2

Abstract

Combination of low-dimensionality and electron correlation is vital for exotic quantum phenomena such as the Mott-insulating phase and high-temperature superconductivity. Transition-metal dichalcogenide (TMD) 1T-TaS2 has evoked great interest owing to its unique nonmagnetic Mott-insulator nature coupled with a charge-density-wave (CDW). To functionalize such a complex phase, it is essential to enhance the CDW-Mott transition temperature TCDW-Mott, whereas this was difficult for bulk TMDs with TCDW-Mott < 200 K. Here we report a strong-coupling 2D CDW-Mott phase with a transition temperature onset of ~530 K in monolayer 1T-TaSe2. Furthermore, the electron correlation derived lower Hubbard band survives under external perturbations such as carrier doping and photoexcitation, in contrast to the bulk counterpart. The enhanced Mott-Hubbard and CDW gaps for monolayer TaSe2 compared to NbSe2, originating in the lattice distortion assisted by strengthened correlations and disappearance of interlayer hopping, suggest stabilization of a likely nonmagnetic CDW-Mott insulator phase well above the room temperature. The present result lays the foundation for realizing monolayer CDW-Mott insulator based devices operating at room temperature.