Evolution from Itinerant Antiferromagnet to Unconventional Superconductor with Fluorine Doping in La(O_{1-x}F_{x})FeAs Revealed by ^{75}As and ^{139}La Nuclear Magnetic Resonance

摘要: We report experimental results of ^{75}As and ^{139}La nuclear magnetic resonance (NMR) in the iron-based layered La(O_{1-x}F_{x})FeAs (x= 0.0, 0.04 0.11) system. In undoped LaOFeAs, 1/T_1 exhibits a distinct peak at T_N ~ 142 K below which spectra become broadened due to internal field attributed an antiferromagnetic (AFM) ordering. 4% F-doped sample, 1/T_1T Curie-Weiss temperature dependence down 30 K, suggesting development AFM spin fluctuations with decreasing temperature. 11% contrast, pseudogap behavior is observed both site gap value ~172 K. The dynamics vary markedly F doping, ascribed Fermi-surface structure. As for superconducting properties samples, compounds does not exhibit coherence just T_c follows T^3 low temperatures, suggests unconventional superconductivity line-nodes. discuss similarities differences between cuprates, also relationship on basis doping 1/T_1.