Exploring the Charge Density Wave Phase of 1T-TaSe2: Mott or Charge-Transfer Gap?

1T-TaSe2 is widely believed to host a Mott metal-insulator transition in the charge density wave (CDW) phase according to the spectroscopic observation of a band gap that extends across all momentum space. Previous investigations inferred that the occurrence of the Mott phase is limited to the surface only of bulk specimens, but recent analysis on thin samples revealed that the Mott-like behavior, observed in the monolayer, is rapidly suppressed with increasing thickness. Here, we report combined time-and angle -resolved photoemission spectroscopy and theoretical investigations of the electronic structure of 1T-TaSe2. Our experimental results confirm the existence of a state above EF, previously ascribed to the upper Hubbard band, and an overall band gap of similar to 0.7 eV at Gamma over bar . However, supported by density functional theory calculations, we demonstrate that the origin of this state and the gap rests on band structure modifications induced by the CDW phase alone, without the need for Mott correlation effects.

Automated summary

1T-TaSe2 is believed to undergo a Mott metal-insulator transition in the CDW phase, characterized by a band gap observed across all momentum space. Previous studies suggested that the Mott phase is limited to the surface of bulk samples, but recent analysis on thin samples showed a rapid suppression of Mott-like behavior with increasing thickness. In this study, combined time-and angle-resolved photoemission spectroscopy and theoretical investigations were conducted on 1T-TaSe2. The experimental results confirmed the presence of a state above EF, previously attributed to the upper Hubbard band, and an overall band gap of around 0.7 eV at Gamma over bar. However, density functional theory calculations demonstrated that the origin of this state and the gap can be explained by band structure modifications induced by the CDW phase alone, without the need for Mott correlation effects.