We present extensive 75As-NMR data on the electron-doped pnictides PrFeAsO 0.89F 0.11 (T c = 45 K), LaFeAsO 0.92F 0.08 (T c = 23 K), and the hole-doped Ba 0.72K 0.28Fe 2As 2 (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.
- Spin fluctuations
- Superconducting gap
ASJC Scopus subject areas
- Electronic, Optical and Magnetic Materials
- Condensed Matter Physics