${\mathrm{FeTe}}_{0.55}{\mathrm{Se}}_{0.45}$ (FTS) occupies a special spot in modern condensed matter physics at the intersections of electron correlation, topology, and unconventional superconductivity. The bulk electronic structure of FTS is predicted to be topologically nontrivial due to the band inversion between the $d_{xz}$ and $p_z$ bands along $\mathrm{\Gamma }\text{−}Z$. However, there remain debates in both the authenticity of the Dirac surface states (DSSs) and the experimental deviations of band structure from the theoretical band inversion picture. Here we resolve these debates through a comprehensive angle-resolved photoemission spectroscopy investigation. We first observe a persistent DSS independent of $k_z$. Then, by comparing FTS with FeSe, which has no band inversion along $\mathrm{\Gamma }\text{−}Z$, we identify the spectral weight fingerprint of both the presence of the $p_z$ band and the inversion between the $d_{xz}$ and $p_z$ bands. Furthermore, we propose a renormalization scheme for the band structure under the framework of a tight-binding model preserving crystal symmetry. Our results highlight the significant influence of correlation on modifying the band structure and make a strong case for the existence of topological band structure in this unconventional superconductor.

中文翻译：

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FeTe0.55Se0.45 拓扑能带结构的轨道成分和持久狄拉克表面态


${\mathrm{FeTe}}_{0.55}{\mathrm{Se}}_{0.45}$ (FTS) 在现代凝聚态物理学中在电子关联、拓扑和非常规超导的交叉领域占据着特殊的地位。由于沿 $\mathrm{\Gamma }\text{−}Z$ 的 $d_{xz}$ 和 $p_z$ 能带之间的能带反转，预计 FTS 的体电子结构在拓扑上并不平凡。然而，狄拉克表面态（DSS）的真实性以及能带结构与理论能带反演图的实验偏差仍然存在争议。在这里，我们通过全面的角度分辨光电子能谱研究来解决这些争论。我们首先观察到独立于 $k_z$ 的持久 DSS。然后，通过将 FTS 与沿 $\mathrm{\Gamma }\text{−}Z$ 没有能带反转的 FeSe 进行比较，我们确定了 $p_z$ 能带的存在和 $d_{xz}$ 和 $p_z$ 波段。此外，我们在保持晶体对称性的紧束缚模型框架下提出了能带结构的重正化方案。我们的结果强调了相关性对改变能带结构的显着影响，并为这种非常规超导体中拓扑能带结构的存在提供了有力的证据。