Possible Superconducting Symmetry and Magnetic Correlations in K0.8Fe2Se2: A 77Se-NMR Study

Abstract

We report ^77Se-NMR measurements in the recent discovered K_0.8Fe_2Se_2 with the superconducting transition temperature T_c=32 K. The characteristic point of this system is that the high density of state is located in the vicinity of the Fermi level. The comparison between Knight shift and nuclear spin lattice relaxation rate 1/T_1 shows that the antiferromagnetic spin correlation is not strong in this system, but it is reasonable to consider that its development toward low temperatures occurs. 1/T_1 in the superconducting state can be reproduced well by an s+- wave model, but a d wave model also roughly reproduces the data. Non exponential behavior in 1/T_1 at low temperatures disagrees with a single isotropic gap.

4 pages, 4 figures, some mistakes were corrected

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• Spin-wave excitations and superconducting resonant mode in Cs(x)Fe(2-y)Se2
• NMR investigation of spin correlations in BaCo2As2
• Superconductivity and normal state properties of single-crystalline Tl0.47Rb0.34Fe1.63Se2 as seen via 77Se and 87Rb NMR
• Electron-phonon coupling in the superconducting single crystal Rb${}_{0.8}$Fe${}_{1.68}$Se${}_2$
• Role of Fermi surface anisotropy in the study of gap anisotropy using magnetic-field-angle dependence of thermal oscillations in AyFe2-xSe2 superconductors
• Weak Spin Fluctuation with Finite Wave Vector and Superconducting Gap Symmetry in KxFe2-ySe2: 77Se Nuclear Magnetic Resonance