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

doi:10.1088/1674-1056/abec37

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 Λ_L. 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 Λ_L and obtain the superconducting gaps of LiFeAs, as

Δ_{1} = 1.2

k_B T_c and

Δ_{2} = 2.8

k_B 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: rzhou@iphy.ac.cn

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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