Normal state above the upper critical field in Fe_1+yTe_1-x(Se,S)_x

Here, we have investigated the magnetotransport above the upper critical field (H_c2) in Fe_1.14 Te_0.7 Se_0.3, Fe_1.02 Te_0.61 Se_0.39, Fe_1.05 Te_0.89 Se_0.11, and Fe_1.06 Te_0.86 S_0.14 . The μ SR measurements confirm electronic phase separation in Fe_1.06 Te_0.86 S_0.14, similar to Fe_1+y Te_1--_x Se_x . We found that superconductivity is suppressed in high magnetic fields above 60 T, allowing us to gain insight into the normal-state properties below the zero-field superconducting transition temperature (T_c). We also show that the resistivity of Fe_1.14 Te_0.7 Se_0.3 and Fe_1.02 Te_0.61 Se_0.39 above H_c2 is metallic as T → 0, just like the normal-state resistivity above T_c . On the other hand, the normal-state resistivity in Fe_1.05 Te_0.89 Se_0.11 and Fe_1.06 Te_0.86 S_0.14 is nonmetallic down to lowest temperatures, reflecting the superconductor-insulator transition due to electronic phase separation.