Author:
Jia 贾 Junjie 俊杰,Gu 谷 Yadong 亚东,Yin 殷 Chaohui 超辉,Shu 束 Yingjie 英杰,Chen 陈 Yiwen 逸雯,Shi 史 Jumin 聚民,Zhang 张 Xing 杏,Chen 陈 Hao 浩,Miao 苗 Taimin 泰民,Ren 任 Xiaolin 晓琳,Liang 梁 Bo 波,Zhu 朱 Wenpei 文培,Cai 蔡 Neng 能,Zhang 张 Fengfeng 丰丰,Zhang 张 Shenjin 申金,Yang 杨 Feng 峰,Wang 王 Zhimin 志敏,Peng 彭 Qinjun 钦军,Xu 许 Zuyan 祖彦,Mao 毛 Hanqing 寒青,Liu 刘 Guodong 国东,Ren 任 Zhian 治安,Zhao 赵 Lin 林,Zhou 周 Xing-Jiang 兴江
Abstract
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 d
yz
band and the topological surface band, making it possible to study their superconducting behaviors separately. The d
yz
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 d
yz
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.