Intrinsic and structural isotope effects in Fe-based superconductors

TL;DR

This paper investigates the isotope effect in Fe-based superconductors, revealing that structural changes due to isotope substitution influence T_c and that, after correction, a consistent isotope effect exponent around 0.35-0.4 is observed across multiple families.

Contribution

It demonstrates that structural effects must be considered when evaluating the isotope effect, leading to a unified understanding of the isotope effect exponent in Fe-based HTS.

Findings

Structural modifications from isotope substitution affect T_c.

Corrected isotope effect exponent is approximately 0.35-0.4.

Consistent isotope effect exponent across different Fe-based superconductor families.

Abstract

The currently available results of the isotope effect on the superconducting transition temperature T_c in Fe-based high-temperature superconductors (HTS) are highly controversial. The values of the Fe isotope effect (Fe-IE) exponent \alpha_Fe 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 \alpha_BCS=0.5. Here we demonstrate that the Fe isotope substitution causes small structural modifications which, in turn, affect T_c. Upon correcting the isotope effect exponent for these structural effects, an almost unique value of \alpha~0.35-0.4 is observed for at least three different families of Fe-based HTS.