Pressure Effects on the Tetragonal FeS Superconductor

High-pressure regulation has played an important role in enhancing the superconducting transition temperature (T_c) and revealing the competing electronic orders and superconducting mechanisms of iron-based superconductors. A large number of high-pressure studies have shown that different pressure conditions (hydrostatic vs. non-hydrostatic pressure) can make great differences in the physical properties of condensed matters under high pressure. To unveil the discrepancies of different high-pressure studies on tetragonal FeS, we performed high-pressure magnetic susceptibility and resistivity measurements on tetragonal FeS single crystal up to 11 GPa by using a piston-cylinder and a cubic anvil cell that can produce good hydrostatic pressures. It is found that its T_c decreases monotonically with increasing pressure with a slope of dT_c/dp≈−1.5 K/GPa, which indicates that the superconductivity can be completely suppressed at about 3 GPa. When the tetragonal-hexagonal structural phase transition occurs at about 4−5 GPa, the temperature-dependent resistivity changes from metallic to semiconducting behavior, and the resistivity shows continuous increase upon further increasing pressure. No second superconducting phase was observed up to 11 GPa, and our results thus do not support the conclusion that FeS has two superconducting phases at high pressure. Finally, in light of the structural information under pressure, we discussed briefly the underlying mechanism for the distinct pressure evolutions of the physical properties in FeS and FeSe.