Anisotropic pressure effects on superconductivity in Fe1+yTe1-xSx

We have investigated uniaxial and hydrostatic pressure effects on superconductivity in Fe1.07Te0.88S0.12 through magnetic-susceptibility measurements down to 1.8 K. The superconducting transition temperature Tc 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, Tc 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 Fe1+yTe1-xSx is enhanced when the lattice constant c considerably shrinks. This implies that the relationship between Tc and the anion height for Fe1+yTe1-xSx is similar to that applicable to most iron-based superconductors. We consider the reduction of Tc by hydrostatic pressure due to suppression of spin fluctuations because the system moves away from antiferromagnetic ordering, and the enhancement of Tc by out-of-plane pressure due to the anion height effect on Tc.