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arXiv · 1605.05184

Strong coupling superconductivity revealed by scanning tunneling microscope in tetragonal FeS

Xiong Yang·Zengyi Du·Guan Du·Qiangqiang Gu·Hai Lin·Delong Fang·Huan Yang·Xiyu Zhu·Hai-Hu Wen
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Abstract

We investigate the electronic properties of the tetragonal FeS superconductor by using scanning tunneling microscope/spectroscopy. It is found that the typical tunneling spectrum on the top layer of sulfur can be nicely fitted with an anisotropic s-wave or a combination of two superconducting components in which one may have a highly anisotropic or nodal like superconducting gap. The fittings lead to the maximum superconducting gap $Δ_{max}\approx$ 0.90$\;$meV, which yields a ratio of 2$Δ_{max}/k_BT_c\approx$ 4.65. This value is larger than that of the predicted value 3.53 by the BCS theory in the weak coupling limit, indicating a strong coupling superconductivity. Two kinds of defects are observed on the surface, which can be assigned to the defects on the S sites (four-fold image) and Fe sites (dumbbell shape). Impurity induced resonance states are found only for the former defects and stay at zero-bias energy.

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Xiong Yang, Zengyi Du, Guan Du, Qiangqiang Gu, Hai Lin, Delong Fang, Huan Yang, Xiyu Zhu, Hai-Hu Wen. 2016-07-27. Strong coupling superconductivity revealed by scanning tunneling microscope in tetragonal FeS. https://doi.org/10.1103/physrevb.94.024521

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