Absence of BCS–BEC crossover in FeSe0.45Te0.55 superconductor
/ Authors
Junjie 俊杰 Jia 贾, Y. Gu 谷, Chaohui 超辉 Yin 殷, Yingjie 英杰 Shu 束, Yiwen 逸雯 Chen 陈, Jumin 聚民 Shi 史, X. Zhang 张, H. Chen 陈, Taimin 泰民 Miao 苗, X. Ren 任
and 14 more authors
B. Liang 梁, Wenpei 文培 Zhu 朱, Neng 能 Cai 蔡, F. Zhang 张, S. Zhang 张, F. Yang 杨, Z. Wang 王, Q. Peng 彭, Z. Xu 许, H. Mao 毛, G. Liu 刘, Z. Ren 任, L. Zhao 赵, X. Zhou 周
/ 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 [Bardeen–Cooper–Schrieffer (BCS), Bose–Einstein condensation (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.
Journal: Chinese Physics B