Absence of BCS-BEC Crossover in FeSe0.45Te0 55 Superconductor

Junjie Jia; Yadong Gu; Chaohui Yin; Yingjie Shu; Yiwen Chen; Jumin Shi; Xing Zhang; Hao Chen; Taimin Miao; Xiaolin Ren; Bo Liang; Wenpei Zhu; Neng Cai; Fengfeng Zhang; Shenjin Zhang; Feng Yang; Zhimin Wang; Qinjun Peng; Zuyan Xu; Hanqing Mao; Guodong Liu; Zhian Ren; Lin Zhao; X. J. Zhou

arXiv · 2407.20771

Absence of BCS-BEC Crossover in FeSe0.45Te0 55 Superconductor

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Abstract

In iron-based superconductor Fe(Se,Te), a flat band-like feature near the Fermi level was observed around the Brillouin zone center in the superconducting state. It is under debate whether this is the evidence on the presence of the BCS-BEC crossover in the superconductor. High-resolution laser-based angle-resolved photoemission measurements are carried out on high quality single crystals of FeSe0.45Te0.55 superconductor to address the issue. By employing different polarization geometries, we have resolved and isolated the dyz band and the topological surface band, making it possible to study their superconducting behaviors separately. The dyz band alone does not form a flat band-like feature in the superconducting state and the measured dispersion can be well described by the BCS picture. We find that the flat band-like feature is formed from the combination of the dyz band and the topological surface state band in the superconducting state. These results reveal the origin of the flat band-like feature and rule out the presence of BCS-BEC crossover in Fe(Se,Te) superconductor.

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Junjie Jia, Yadong Gu, Chaohui Yin, Yingjie Shu, Yiwen Chen, Jumin Shi, Xing Zhang, Hao Chen, Taimin Miao, Xiaolin Ren, Bo Liang, Wenpei Zhu, Neng Cai, Fengfeng Zhang, Shenjin Zhang, Feng Yang, Zhimin Wang, Qinjun Peng, Zuyan Xu, Hanqing Mao, Guodong Liu, Zhian Ren, Lin Zhao, X. J. Zhou. 2024-07-30. Absence of BCS-BEC Crossover in FeSe0.45Te0 55 Superconductor. https://arxiv.org/abs/2407.20771

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