Weakening of the diamagnetic shielding in FeSe1-xSx at high pressures

The superconducting transition of FeSe1-xSx with three distinct sulfur concentrations x was studied under hydrostatic pressures up to similar to 70 kbar via bulk ac susceptibility. The pressure dependence of the superconducting transition temperature (T-c) features a small dome-shaped variation at low pressures for x = 0.04 and x = 0.12, followed by a more substantial T-c enhancement to a value of around 30 K at moderate pressures. In x = 0.21, a similar overall pressure dependence of T-c is observed, except that the small dome at low pressures is flattened. For all three concentrations, a significant weakening of the diamagnetic shielding is observed beyond the pressure around which the maximum T-c of 30 K is reached near the verge of the pressure-induced magnetic phase. This observation points to a strong competition between the magnetic and high-T-c superconducting states at high pressure in this system.