77Se-NMR Study under Pressure on 12%-S Doped FeSe

The 12%-S doped FeSe system has a high T-c of 30K at a pressure of 3.0 GPa. We have successfully investigated its microscopic properties for the first time via Se-77-NMR measurements under pressure. The antiferromagnetic (AFM) fluctuations at the optimal pressure (similar to 3 GPa) exhibited unexpected suppression compared with the AFM fluctuations at ambient pressure, even though the optimal pressure is close to the phase boundary of the AFM phase induced at the high-pressure region. In addition, we revealed that the SC phase at an applied field of 6.02 T exhibited a remarkable double-dome structure in the pressure temperature phase diagram, unlike the SC phase at zero field.