Genuine electronic structure and superconducting gap structure in (Ba0.6K0.4)Fe2As2 superconductor

Yongqing Cai; Jianwei Huang; Taimin Miao; Dingsong Wu; Qiang Gao; Cong Li; Yu Xu; Junjie Jia; Qingyan Wang; Yuan Huang; Guodong Liu; Fengfeng Zhang; Shenjin Zhang; Feng Yang; Zhimin Wang; Qinjun Peng; Zuyan Xu; Lin Zhao; Xingjiang Zhou

doi:10.1016/j.scib.2021.05.015

Genuine electronic structure and superconducting gap structure in (Ba_0.6K_0.4)Fe₂As₂ superconductor

Sci Bull (Beijing). 2021 Sep 30;66(18):1839-1848. doi: 10.1016/j.scib.2021.05.015. Epub 2021 May 19.

Authors

Yongqing Cai¹, Jianwei Huang², Taimin Miao¹, Dingsong Wu¹, Qiang Gao¹, Cong Li¹, Yu Xu¹, Junjie Jia¹, Qingyan Wang³, Yuan Huang³, Guodong Liu³, Fengfeng Zhang⁴, Shenjin Zhang⁴, Feng Yang⁴, Zhimin Wang⁴, Qinjun Peng⁴, Zuyan Xu⁴, Lin Zhao⁵, Xingjiang Zhou⁶

Affiliations

¹ National Laboratory for Superconductivity, Beijing National Laboratory for Condensed Matter Physics, Institute of Physics, Chinese Academy of Sciences, Beijing 100190, China; University of Chinese Academy of Sciences, Beijing 100049, China.
² National Laboratory for Superconductivity, Beijing National Laboratory for Condensed Matter Physics, Institute of Physics, Chinese Academy of Sciences, Beijing 100190, China.
³ National Laboratory for Superconductivity, Beijing National Laboratory for Condensed Matter Physics, Institute of Physics, Chinese Academy of Sciences, Beijing 100190, China; University of Chinese Academy of Sciences, Beijing 100049, China; Songshan Lake Materials Laboratory, Dongguan 523808, China.
⁴ Technical Institute of Physics and Chemistry, Chinese Academy of Sciences, Beijing 100190, China.
⁵ National Laboratory for Superconductivity, Beijing National Laboratory for Condensed Matter Physics, Institute of Physics, Chinese Academy of Sciences, Beijing 100190, China; University of Chinese Academy of Sciences, Beijing 100049, China; Songshan Lake Materials Laboratory, Dongguan 523808, China. Electronic address: lzhao@iphy.ac.cn.
⁶ National Laboratory for Superconductivity, Beijing National Laboratory for Condensed Matter Physics, Institute of Physics, Chinese Academy of Sciences, Beijing 100190, China; University of Chinese Academy of Sciences, Beijing 100049, China; Songshan Lake Materials Laboratory, Dongguan 523808, China; Beijing Academy of Quantum Information Sciences, Beijing 100193, China. Electronic address: XJZhou@iphy.ac.cn.

PMID: 36654393
DOI: 10.1016/j.scib.2021.05.015

Abstract

The electronic structure and superconducting gap structure are prerequisites to establish microscopic theories in understanding the superconductivity mechanism of iron-based superconductors. However, even for the most extensively studied optimally-doped (Ba_0.6K_0.4)Fe₂As₂, there remain outstanding controversies on its electronic structure and superconducting gap structure. Here we resolve these issues by carrying out high-resolution angle-resolved photoemission spectroscopy (ARPES) measurements on the optimally-doped (Ba_0.6K_0.4)Fe₂As₂ superconductor using both Helium lamp and laser light sources. Our results indicate the "flat band" feature observed around the Brillouin zone center in the superconducting state originates from the combined effect of the superconductivity-induced band back-bending and the folding of a band from the zone corner to the center. We found direct evidence of the band folding between the zone corner and the center in both the normal and superconducting state. Our resolution of the origin of the flat band makes it possible to assign the three hole-like bands around the zone center and determine their superconducting gap correctly. Around the zone corner, we observe a tiny electron-like band and an M-shaped band simultaneously in both the normal and superconducting states. The obtained gap size for the bands around the zone corner (~5.5 meV) is significantly smaller than all the previous ARPES measurements. Our results establish a new superconducting gap structure around the zone corner and resolve a number of prominent controversies concerning the electronic structure and superconducting gap structure in the optimally-doped (Ba_0.6K_0.4)Fe₂As₂. They provide new insights in examining and establishing theories in understanding superconductivity mechanism in iron-based superconductors.

Keywords: (Ba(0.6)K(0.4))Fe(2)As(2); ARPES; Band folding; Electronic structure; Superconducting gap.