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探索 1T-TaSe_{2}的电荷密度波相:莫特绝缘或电荷转移能隙?

Exploring the Charge Density Wave Phase of 1T-TaSe_{2}: Mott or Charge-Transfer Gap?

机构信息

Dipartimento di Fisica, Politecnico di Milano, Milan 20133, Italy.

STFC Central Laser Facility, Research Complex at Harwell, Harwell Campus, Didcot OX11 0QX, United Kingdom.

出版信息

Phys Rev Lett. 2023 Apr 14;130(15):156401. doi: 10.1103/PhysRevLett.130.156401.

Abstract

1T-TaSe_{2} 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-TaSe_{2}. Our experimental results confirm the existence of a state above E_{F}, previously ascribed to the upper Hubbard band, and an overall band gap of ∼0.7  eV at Γ[over ¯]. 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.

摘要

1T-TaSe_{2} 根据在整个动量空间延伸的带隙的光谱观察,被广泛认为在电荷密度波(CDW)相中存在莫特金属-绝缘体转变。先前的研究推断莫特相的发生仅局限于体样品的表面,但对薄样品的最近分析表明,在单层中观察到的类莫特行为随着厚度的增加而迅速被抑制。在这里,我们报告了对 1T-TaSe_{2} 的电子结构的时间和角度分辨光发射光谱学和理论研究的综合结果。我们的实验结果证实了在 E_{F}上方存在一个状态,之前归因于上 Hubbard 带,并且在 Γ[over ¯]处的整体带隙约为 0.7  eV。然而,基于密度泛函理论计算,我们证明了这个状态和带隙的起源是由 CDW 相单独引起的能带结构的改变,而不需要莫特相关效应。

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