The currently available results of the isotope effect on the superconducting transition temperature Tc in Fe-based high-temperature superconductors (HTSs) are highly controversial. The values of the Fe isotope effect exponent αFe for various families of Fe-based HTS were found to be as well positive, as negative, or even be exceedingly larger than the BCS value αBCS≡0.5. Here we emphasize that the Fe isotope substitution causes small structural modifications which, in turn, affect Tc. Upon correcting the isotope effect exponent for these structural effects, an almost unique value of α∼0.35–0.4 is observed for at least three different families of Fe-based HTS.
© 2010 The American Physical Society