Author/Authors :
Z. Li، نويسنده , , S. Kawasaki، نويسنده , , T. Oka، نويسنده , , T. Tabuchi، نويسنده , , Y. Ooe، نويسنده , , M. Ichioka، نويسنده , , Z.A. Ren، نويسنده , , Z.X. Zhao، نويسنده , , J.L. Luo، نويسنده , , N.L. Wang، نويسنده , , X.C. Wang، نويسنده , , Q.Q. Liu، نويسنده , , C.Q. Jin، نويسنده , , C.T. Lin، نويسنده , , Guoqing Zheng، نويسنده ,
Abstract :
We present extensive 75As NMR and NQR data on the superconducting arsenides PrFeAs0.89F0.11View the MathML source(Tc=45K), LaFeAsO0.92F0.08View the MathML source(Tc=27K), LiFeAs View the MathML source(Tc=17K) and Ba0.72K0.28Fe2As2View the MathML source(Tc=31.5K) single crystal, and compare with the nickel analog LaNiAsO0.9F0.1View the MathML source(Tc=4.0K). In contrast to LaNiAsO0.9F0.1 where the superconducting gap is shown to be isotropic, the spin lattice relaxation rate 1/T1 in the Fe-arsenides decreases below Tc with no coherence peak and shows a step-wise variation at low temperatures. The Knight shift decreases below Tc and shows a step-wise T variation as well. These results indicate spin-singlet superconductivity with multiple gaps in the Fe-arsenides. The Fe antiferromagnetic spin fluctuations are anisotropic and weaker compared to underdoped copper-oxides or cobalt-oxide superconductors, while there is no significant electron correlations in LaNiAsO0.9F0.1. We will discuss the implications of these results and highlight the importance of the Fermi surface topology.
