Chin. Phys. Lett.  2022, Vol. 39 Issue (5): 057302    DOI: 10.1088/0256-307X/39/5/057302
Unusual Band Splitting and Superconducting Gap Evolution with Sulfur Substitution in FeSe
Yuanyuan Yang1, Qisi Wang2, Shaofeng Duan1, Hongliang Wo2, Chaozhi Huang1, Shichong Wang1, Lingxiao Gu1, Dong Qian1, Jun Zhao2,3, and Wentao Zhang1*
1Key Laboratory of Artificial Structures and Quantum Control (Ministry of Education), Shenyang National Laboratory for Materials Science, School of Physics and Astronomy, Shanghai Jiao Tong University, Shanghai 200240, China
2State Key Laboratory of Surface Physics and Department of Physics, Fudan University, Shanghai 200433, China
3Institute of Nanoelectronics and Quantum Computing, Fudan University, Shanghai 200433, China
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Yuanyuan Yang, Qisi Wang, Shaofeng Duan et al  2022 Chin. Phys. Lett. 39 057302
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Abstract High-resolution angle-resolved photoemission measurements were taken on FeSe$_{1-x}$S$_x$ ($x$ = 0, 0.04, and 0.08) superconductors. With an ultrahigh energy resolution of 0.4 meV, unusual two hole bands near the Brillouin-zone center, which was possibly a result of additional symmetry breaking, were identified in all the sulfur-substituted samples. In addition, in both of the hole bands highly anisotropic superconducting gaps with resolution limited nodes were evidenced. We find that the larger superconducting gap on the outer hole band is reduced linearly to the nematic transition temperature while the gap on the inner hole is nearly S-substitution independent. Our observations strongly suggest that the superconducting gap increases with enhanced nematicity although the superconducting transition temperature is not only governed by the pairing strength, demonstrating strong constraints on theories in the FeSe family.
Received: 18 March 2022      Express Letter Published: 23 April 2022
PACS:  74.20.Rp (Pairing symmetries (other than s-wave))  
  74.25.Jb (Electronic structure (photoemission, etc.))  
  74.70.Xa (Pnictides and chalcogenides)  
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Yuanyuan Yang
Qisi Wang
Shaofeng Duan
Hongliang Wo
Chaozhi Huang
Shichong Wang
Lingxiao Gu
Dong Qian
Jun Zhao
and Wentao Zhang
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