Browsing by Author "Pfau, H."

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    Nematic Energy Scale and the Missing Electron Pocket in FeSe
    (American Physical Society, 2019) Yi, M.; Pfau, H.; Zhang, Y.; He, Y.; Wu, H.; Chen, T.; Ye, Z.R.; Hashimoto, M.; Yu, R.; Si, Q.; Lee, D.-H.; Dai, Pengcheng; Shen, Z.-X.; Lu, D.H.; Birgeneau, R.J.
    Superconductivity emerges in proximity to a nematic phase in most iron-based superconductors. It is therefore important to understand the impact of nematicity on the electronic structure. Orbital assignment and tracking across the nematic phase transition prove to be challenging due to the multiband nature of iron-based superconductors and twinning effects. Here, we report a detailed study of the electronic structure of fully detwinned FeSe across the nematic phase transition using angle-resolved photoemission spectroscopy. We clearly observe a nematicity-driven band reconstruction involving dxz, dyz, and dxy orbitals. The nematic energy scale between dxz and dyz bands reaches a maximum of 50 meV at the Brillouin zone corner. We are also able to track the dxz electron pocket across the nematic transition and explain its absence in the nematic state. Our comprehensive data of the electronic structure provide an accurate basis for theoretical models of the superconducting pairing in FeSe.
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    Orbital Ingredients and Persistent Dirac Surface State for the Topological Band Structure in ${\mathrm{FeTe}}_{0.55}{\mathrm{Se}}_{0.45}$
    (American Physical Society, 2024) Li, Y.-F.; Chen, S.-D.; García-Díez, M.; Iraola, M. I.; Pfau, H.; Zhu, Y.-L.; Mao, Z.-Q.; Chen, T.; Yi, M.; Dai, P.-C.; Sobota, J. A.; Hashimoto, M.; Vergniory, M. G.; Lu, D.-H.; Shen, Z.-X.
    FeTe0.55⁢Se0.45 (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 𝑑𝑥⁢𝑧 and 𝑝𝑧 bands along Γ−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 𝑘𝑧. Then, by comparing FTS with FeSe, which has no band inversion along Γ−𝑍, we identify the spectral weight fingerprint of both the presence of the 𝑝𝑧 band and the inversion between the 𝑑𝑥⁢𝑧 and 𝑝𝑧 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.