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Chin. Phys. B, 2021, Vol. 30(4): 047403    DOI: 10.1088/1674-1056/abec37

Nodal superconducting gap in LiFeP revealed by NMR: Contrast with LiFeAs

A F Fang(房爱芳)1, R Zhou(周睿)2,3,†, H Tukada4, J Yang(杨杰)2, Z Deng(邓正)2, X C Wang(望贤成)2, C Q Jin(靳常青)2, and Guo-Qing Zheng(郑国庆)2,4
1 Department of Physics, Beijing Normal University, Beijing 100875, China;
2 Institute of Physics, Chinese Academy of Sciences, and Beijing National Laboratory for Condensed Matter Physics, Beijing 100190, China;
3 Songshan Lake Materials Laboratory, Dongguan 523808, China;
4 Department of Physics, Okayama University, Okayama 700-8530, Japan
Abstract  Identifying the uniqueness of FeP-based superconductors may shed new lights on the mechanism of superconductivity in iron-pnictides. Here, we report nuclear magnetic resonance (NMR) studies on LiFeP and LiFeAs which have the same crystal structure but different pnictogen atoms. The NMR spectrum is sensitive to inhomogeneous magnetic fields in the vortex state and can provide the information on the superconducting pairing symmetry through the temperature dependence of London penetration depth ΛL. We find that Λ L saturates below T ∼ 0.2 T c in LiFeAs, where T c is the superconducting transition temperature, indicating nodeless superconducting gaps. Furthermore, by using a two-gaps model, we simulate the temperature dependence of ΛL and obtain the superconducting gaps of LiFeAs, as $\varDelta_1 = 1.2$ kB Tc and $\varDelta_2 = 2.8$ kB T c, in agreement with previous result from spin-lattice relaxation. For LiFeP, in contrast, Λ L does not show any saturation down to T ∼ 0.03 T c, indicating nodes in the superconducting gap function. Finally, we demonstrate that strong spin fluctuations with diffusive characteristics exist in LiFeP, as in some cuprate high temperature superconductors.
Keywords:  iron-based superconductor      nuclear magnetic resonance      superconducting pairing symmetry      spin fluctuations  
Received:  10 January 2021      Revised:  05 February 2021      Accepted manuscript online:  05 March 2021
PACS:  74.70.Xa (Pnictides and chalcogenides)  
  74.25.nj (Nuclear magnetic resonance)  
  74.20.Rp (Pairing symmetries (other than s-wave))  
  75.40.Gb (Dynamic properties?)  
Fund: Project supported by the Natioanl Natural Science Foundation of China (Grant Nos. 11904023, 11974405, 11674377, and 11634015), the Fundamental Research Funds for the Central Universities, China (Grant No. 2018NTST22), the National Key R&D Program of China (Grant Nos. 2016YFA0300502 and 2017YFA0302904), and the Strategic Priority Research Program of the Chinese Academy of Sciences (Grant No. XDB33010100).
Corresponding Authors:  Corresponding author. E-mail:   

Cite this article: 

A F Fang(房爱芳), R Zhou(周睿), H Tukada, J Yang(杨杰), Z Deng(邓正), X C Wang(望贤成) , C Q Jin(靳常青), and Guo-Qing Zheng(郑国庆) Nodal superconducting gap in LiFeP revealed by NMR: Contrast with LiFeAs 2021 Chin. Phys. B 30 047403

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