Anisotropic spin fluctuations and multiple superconducting gaps in hole-doped Ba0.72K0.28Fe2As2: NMR in a single crystalK. Matano1, Z. Li1, G. L. Sun2, D. L. Sun2, C. T. Lin2, M. Ichioka1 and Guo-qing Zheng1, 3
1 Department of Physics, Okayama University - Okayama 700-8530, Japan
2 Max Planck Institute - Heisenbergstrasse 1, D-70569 Stuttgart, Germany, EU
3 Institute of Physics, Chinese Academy of Sciences - Beijing 100190, China
received 1 July 2009; accepted in final form 17 July 2009; published July 2009
published online 18 August 2009
We report the 75As-NMR study on a single crystal of the hole-doped iron-pnictide superconductor Ba0.72K0.28Fe2As2 ( Tc = 31.5 K). 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/T1 decreases below Tc with no coherence peak and shows a stepwise variation at low temperatures, which is indicative of multiple superconducting gaps, as in the electron-doped Pr(La)FeAsO1- xFx. Furthermore, no evidence was obtained for a microscopic coexistence of a long-range magnetic order and superconductivity.
74.20.Rp - Pairing symmetry (other than s-wave).
74.25.Jb - Electronic structure.
74.25.Nf - Response to electromagnetic fields (nuclear magnetic resonance, surface impedance, etc.).
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