Anisotropic pressure effects on superconductivity in Fe_1+yTe_1−xS_x

We have investigated the uniaxial and hydrostatic pressure effects on superconductivity in Fe_1.07Te_0.88S_0.12 through magnetic susceptibility measurements down to 1.8 K. The superconducting transition temperature T_c is enhanced by out-of-plane pressure (uniaxial pressure along the c-axis); the onset temperature of the superconductivity reaches 11.8 K at 0.4 GPa. In contrast, T_c is reduced by in-plane pressure (uniaxial pressure along the ab-plane) and hydrostatic pressure. Taking into account these results, it is inferred that the superconductivity of Fe_1+yTe₁−_xS_x is enhanced when the lattice constant c considerably decreases. This implies that the relationship between T_c and the anion height for Fe_1+yTe₁−_xS_x is similar to that for most iron-based superconductors. We consider the reduction of T_c by hydrostatic pressure to be due to the suppression of spin fluctuations because the system moves away from antiferromagnetic ordering, and the enhancement of T_c by out-of-plane pressure to be due to the anion height effect on T_c.