Observation of Superconductivity in Tetragonal FeS

The possibility of superconductivity
in tetragonal FeS has attracted
considerable interest because of its similarities to the FeSe superconductor.
However, all efforts made to pursue superconductivity in tetragonal
FeS have failed so far, and it remains controversial whether tetragonal
FeS is metallic or semiconducting. Here we report the observation
of superconductivity at 5 K in tetragonal FeS that is synthesized
by the hydrothermal reaction of iron powder with sulfide solution.
The obtained samples are highly crystalline and less air-sensitive,
in contrast to those reported in the literature, which are meta-stable
and air-sensitive. Magnetic and electrical properties measurements
show that the samples behave as a paramagnetic metal in the normal
state and exhibit superconductivity below 5 K. The high crystallinity
and the stoichiometry of the samples play important roles in the observation
of superconductivity. The present results demonstrate that tetragonal
FeS is a promising new platform to realize high-temperature superconductors.