二维半导体和金属中库仑相互作用的非常规屏蔽：MX2（M=Mo、W、Nb、Ta；X=S、Se、Te）的全面cRPA研究
Nonconventional screening of Coulomb interaction in two-dimensional semiconductors and metals: A comprehensive cRPA study of MX2 (M=Mo, W, Nb, Ta; X=S, Se, Te)
AI总结：
该研究利用第一性原理与cRPA系统计算MX2三种相的d电子库仑参数，揭示短程强屏蔽、长程仍显著的非常规机制，并支持CDW体系的强关联Mott相。
摘要：
在二维半导体性过渡金属二硫化物（TMDs）中，实验观测到的大激子结合能和非氢样里德伯级数，以及二维金属性TMDs中等离子体激元色散的偏差，均表明存在库仑相互作用的非常规屏蔽。在含有4d和5d元素的TMDs的电荷密度波（CDW）重构晶格中，实验观测到的Mott绝缘态进一步证实了这些体系中存在强库仑相互作用。在本研究中，我们采用第一性原理电子结构计算和约束无规相近似（cRPA），计算二维TMDs中局域d电子之间的库仑相互作用参数（部分屏蔽的U和完全屏蔽的W）。我们专门研究了化学式为MX2（M=Nb、Ta、Mo、W，X=S、Se、Te）的材料，并考虑了三种不同的相（1H、1T和1T'）。结果表明，短程相互作用在所有三种相中均受到强烈屏蔽，而长程相互作用即使在金属体系中仍然显著。这种非常规屏蔽为二维半导体性和金属性TMDs中分别观测到的通常氢样里德伯级数和常规等离子体激元色散的偏差提供了有说服力的解释。我们的计算给出1H、1T和1T'结构的在位库仑相互作用参数U分别处于0.8–2.5 eV、0.8–1.9 eV和0.9–2.4 eV范围内。此外，研究结果表明，CDW TMDs中在位有效库仑相互作用与带宽之比显著较高（U_eff/W_b >> 1），为实验观测到的强关联Mott相提供了有力证据。
英文摘要：
Experimental observations of large exciton binding energies and non-hydrogenic Rydberg series in 2D semiconducting TMDs, along with deviations in plasmon dispersion in 2D metallic TMDs, suggest the presence of a nonconventional screening of the Coulomb interaction. The experimentally observed Mott insulating state in the charge density wave (CDW) reconstructed lattice of TMDs containing 4d and 5d elements further confirms the presence of strong Coulomb interactions in these systems. In this study, we use first-principles electronic structure calculations and constrained random-phase approximation to calculate the Coulomb interaction parameters (partially screened U and fully screened W) between localized $d$ electrons in 2D TMDs. We specifically explore materials represented by the formula MX2 (M=Nb, Ta, Mo, W, and X=S, Se, Te) and consider three different phases (1H, 1T, and 1T'). Our results show that the short-range interactions are strongly screened in all three phases, whereas the long-range interactions remain significant even in metallic systems. This nonconventional screening provides a compelling explanation for the deviations observed in the usual hydrogenic Rydberg series and conventional plasmon dispersion in 2D semiconducting and metallic TMDs, respectively. Our calculations yield on-site Coulomb interaction parameters U within the ranges of 0.8-2.5 eV, 0.8-1.9 eV, and 0.9-2.4 eV for the 1H, 1T, and 1T' structures, respectively. Furthermore, our findings indicate a substantially high ratio of on-site effective Coulomb interaction to bandwidth (U_eff/W_b >> 1) in CDW TMDs, providing robust evidence for the experimentally observed strongly correlated Mott phase.
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