Evolution from Itinerant Antiferromagnet to Unconventional Superconductor with Fluorine Doping in LaFeAs(O<SUB>1−<I>x</I></SUB>F<I><SUB>x</SUB></I>) Revealed by <SUP>75</SUP>As and <SUP>139</SUP>La Nuclear Magnetic Resonance

DOI DOI Web Site Web Site BIBCODE 74 Citations 28 References Open Access
  • Nakai Yusuke
    Department of Physics, Graduate School of Science, Kyoto University
  • Ishida Kenji
    Department of Physics, Graduate School of Science, Kyoto University
  • Kamihara Yoichi
    ERATO-SORST, JST, Frontier Collaborative Research Center, Tokyo Institute of Technology
  • Hirano Masahiro
    ERATO-SORST, JST, Frontier Collaborative Research Center, Tokyo Institute of Technology Frontier Research Center, Tokyo Institute of Technology
  • Hosono Hideo
    ERATO-SORST, JST, Frontier Collaborative Research Center, Tokyo Institute of Technology Frontier Research Center, Tokyo Institute of Technology Materials and Structures Laboratory, Tokyo Institute of Technology

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  • Evolution from itinerant antiferromagnet to unconventional superconductor with fluorine doping in LaFeAs(O[1-x]Fx) revealed by 75As and 139La nuclear magnetic resonance
  • Evolution from Itinerant Antiferromagnet to Unconventional Superconductor with Fluorine Doping in LaFeAs(O<sub>1-<i>x</i></sub>F<sub><i>x</i></sub>) Revealed by <sup>75</sup>As and <sup>139</sup>La Nuclear Magnetic Resonance

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We report experimental results of 75As and 139La nuclear magnetic resonance (NMR) in the iron-based layered LaFeAs(O1−xFx) (x=0.0, 0.04, and 0.11). In the undoped LaFeAsO, 1⁄T1 of 139La exhibits a distinct peak at TN∼142 K below which the spectra become broadened due to the internal magnetic field attributed to an antiferromagnetic (AFM) ordering. In the 4% F-doped sample, 1⁄T1T exhibits a Curie–Weiss temperature dependence down to 30 K, suggesting the development of AFM spin fluctuations with decreasing temperature. In the 11% F-doped sample, in contrast, pseudogap behavior is observed in 1⁄T1T both at the 75As and 139La site with a gap value of ΔPG∼172 K. The spin dynamics vary markedly with F doping, which is ascribed to the Fermi-surface structure. As for the superconducting properties for the 4 and 11% F-doped samples, 1⁄T1 in both compounds does not exhibit a coherence peak just below Tc and follows a T3 dependence at low temperatures, which suggests unconventional superconductivity with line-nodes. We discuss similarities and differences between LaFeAs(O1−xFx) and cuprates, and also discuss the relationship between spin dynamics and superconductivity on the basis of F doping dependence of Tc and 1⁄T1.

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