Multiple Superconducting Gaps and Anisotropic Spin Fluctuations in Hole-Doped and Electron-Doped Iron-Pnictides: NMR Studies

Guo-qing Zheng
K. Matano
S. Kawasaki
Z. Li
G. L. Sun
D. L. Sun
C. T. Lin
G. F. Chen
J. L. Luo
N. L. Wang
Z. A. Ren
Z. X. Zhao

We present extensive As-75-NMR data on the electron-doped pnictides PrFeAsO0.89F0.11 (T-c = 45 K), LaFeAsO0.92F0.08 (T-c = 23 K), and the hole-doped Ba0.72K0.28Fe2As2 (T-c = 31.5 K) single crystal. We find that the Fe antiferromagnetic spin fluctuations are anisotropic and are weaker compared to underdoped copper-oxides or cobalt-oxide superconductors. The spin lattice relaxation rate 1 / T-1 decreases below T-c with no coherence peak and shows a step-wise variation at low temperatures. The Knight shift decreases below T-c and shows a step-wise T variation as well. These results indicate spin-singlet superconductivity with multiple gaps.

Journal of Superconductivity and Novel Magnetism

SPRINGER

23

5

609

612

10.1007/s10948-010-0749-1

https://doi.org/10.1007/s10948-010-0749-1
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