Using high-resolution angle-resolved photoemission spectroscopy (ARPES), we systematically studied the electronic structures of quasi-one-dimensional (1D) ternary material Ta₂NiS₅ single crystals. Contrary to its sister compound Ta₂NiSe₅, which is a candidate material for excitonic insulators, we found that Ta₂NiS₅ cannot realize the ground state of an excitonic insulator according to temperature-dependent valence band dispersions along the Γ–X direction. In particular, the experimental ARPES data reveal that the electronic structures show strong two-dimensional characteristics along with a considerable in-plane anisotropy indicating evident coupling among the one-dimensional chain structures. Moreover, theoretical band calculations have to be compressed by a factor of about 15% in energy in order to match the experimental band structures, implying that some weak electron correlations are neglected in the band calculations.

中文翻译：

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高分辨率角分辨光发射光谱揭示 层状Ta ₂ NiS ₅单晶的 电子结构

我们使用高分辨率角分辨光发射光谱（ARPES），系统地研究了准一维（1D）三元材料Ta ₂ NiS ₅单晶的电子结构。相反，它的姐妹化合物的Ta ₂ NISE ₅，其是用于激子绝缘体的候选材料中，我们发现的Ta ₂的NiS ₅可以根据沿着依赖于温度的价带不分散体的实现激子绝缘体的基态Γ - X方向。特别是，实验性ARPES数据表明，电子结构显示出强大的二维特性，并具有明显的面内各向异性，表明一维链结构之间存在明显的耦合。此外，理论带计算必须以大约15％的能量压缩，以匹配实验带结构，这意味着在带计算中忽略了一些弱的电子相关性。