A large iron isotope effect in SmFeAsO(1 - x)F(x) and Ba(1 - x)K(x)Fe(2)As(2).
作者： RH Liu , T Wu , G Wu , H Chen , XF Wang
DOI: 10.1038/NATURE07981
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摘要: The recent discovery of superconductivity in oxypnictides with a critical transition temperature (T-C) higher than the McMillan limit 39K (the theoretical maximum predicted by Bardeen-Cooper-Schrieffer theory) has generated great excitement(1-5). Theoretical calculations indicate that electron-phonon interaction is not strong enough to give rise such high temperatures(6), but ferromagnetic/antiferromagnetic fluctuations have been proposed be responsible(7-9). Superconductivity and magnetism pnictide superconductors, however, show sensitivity crystal lattice, suggesting possibility unconventional coupling. Here we report effect oxygen iron isotope substitution on T-C spin-density wave (SDW) (T-SDW) SmFeAsO1-xFx Ba1-xKxFe2As2 systems. T-SDW very small, while exponent alpha(C) =-dlnT(C)/dlnM about 0.35 (0.5 corresponds full effect). Surprisingly, exchange shows same as T-C. This indicates plays some role superconducting mechanism, simple coupling mechanism seems unlikely because magnon-phonon included.
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