High-Tc Nodeless s_\pm-wave Superconductivity in (Y,La)FeAsO_{1-y} with Tc=50 K: 75As-NMR Study

Abstract

We report 75As-NMR study on the Fe-pnictide high-Tc superconductor Y0.95La0.05FeAsO_{1-y} (Y0.95La0.051111) with Tc=50 K that includes no magnetic rare-earth elements. The measurement of the nuclear-spin lattice-relaxation rate 75(1/T1) has revealed that the nodeless bulk superconductivity takes place at Tc=50 K while antiferromagnetic spin fluctuations (AFSFs) develop moderately in the normal state. These features are consistently described by the multiple fully-gapped s_\pm-wave model based on the Fermi-surface (FS) nesting. Incorporating the theory based on band calculations, we propose that the reason that Tc=50 K in Y0.95La0.051111 is larger than Tc=28 K in La1111 is that the FS multiplicity is maximized, and hence the FS nesting condition is better than that in La1111.

4 pages, 3 figures, accepted for publication in Phys Rev. Lett

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• NMR evidence for an intimate relationship between antiferromagnetic spin fluctuations and extended s-wave superconductivity in mono-crystalline SrFe2(As_{1-x}P_{x})2
• High-$T_c$ Iron-phosphide Superconductivity Enhanced by Reemergent Antiferromagnetic Spin Fluctuations in (Sr${}_4$Sc${}_2$O${}_6$)Fe${}_2$(As${}_{1-x}$P${}_x$)${}_2$ probed by NMR
• Unconventional Multi-gap Superconductivity and Antiferromagnetic Spin Fluctuations in New Iron-arsenide LaFe2As2 in Heavily Electron-doped Regime