AI 中文总结
本研究利用高分辨角分辨光电子能谱证实TiSe2的CDW相变由晶格对称性破缺重构主导，而非电子带隙打开，其体态带隙在相变前后保持鲁棒性。
AI 中文摘要
TiSe2中驱动电荷密度波（CDW）相变的机制已争论数十年，相关提案从激子绝缘体到晶格驱动的不稳定性不等。一个核心问题是该相变是否涉及体态带隙的打开或增强。利用高分辨角分辨光电子能谱，我们直接追踪了在T_CDW=200K处CDW相变前后体态带边的温度演化。与相变会打开带隙的预期相反，我们发现从高温正常相到160K，基本带隙的大小保持恒定。尽管CDW会诱导明显的带折叠特征和谱重再分布，但基础带极值未受扰动。这些结果表明TiSe2不会发生温度驱动的电子带隙打开，反而支持这样的场景：该相变由晶格对称性破缺重构主导，该重构会折叠但不会打开预存带绝缘体的电子结构。
英文摘要
The mechanism driving the charge density wave (CDW) transition in TiSe2 has been debated for decades, with proposals ranging from an excitonic insulator to a lattice-driven instability. A central question remains whether the transition involves an opening or enhancement of the bulk band gap. Using high-resolution angle-resolved photoemission spectroscopy, we directly track the temperature evolution of the bulk band edges across the CDW transition at TCDW = 200 K. Contrary to the expectation of a gap-opening transition, we find that the size of the fundamental band gap remains constant from the high-temperature normal phase down to 160 K. While the CDW induces clear band-folding signatures and spectral weight redistribution, the underlying band extrema are unperturbed. These results demonstrate that TiSe2 does not undergo a temperature-driven electronic gap opening. Instead, they support a scenario where the transition is governed by a lattice symmetry-breaking reconstruction that folds, but does not gap, the electronic structure of a pre-existing band insulator.
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