Iron isotope effect on the superconducting transition temperature and the crystal structure of FeSe1-x

The Fe isotope effect (Fe-IE) on the transition temperature T-c and the crystal structure was studied in the Fe chalcogenide superconductor FeSe1-x by means of magnetization and neutron powder diffraction (NPD). The substitution of natural Fe (containing similar or equal to 92% of Fe-56) by its lighter Fe-54 isotope leads to a shift in T-c of 0.22(5) K corresponding to an Fe-IE exponent of alpha(Fe) = 0.81(15). Simultaneously, a small structural change with isotope substitution is observed by NPD, which may contribute to the total Fe isotope shift of T-c.