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...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 kB 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.展开更多
基金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)+1 种基金the National Key R&D Program of China(Grant Nos.2016YFA0300502 and2017YFA0302904)the Strategic Priority Research Program of the Chinese Academy of Sciences(Grant No.XDB33010100)。
文摘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 kB 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.
