Moisture-induced superconductivity in FeTe0.8S0.2

Moisture-induced superconductivity was observed in FeTe0.8S0.2. With exposing the sample to the air, the zero resistivity temperature and the superconducting volume fraction were enhanced up to 7.2 K and 48.5 %, respectively, while the as-grown sample showed only filamentary superconductivity. We concluded that the causes of the evolution of superconductivity were water-related ions and/or molecules, because only the sample kept in water at room temperature for several days showed superconductivity. The speed of evolution of superconductivity was strongly enhanced by immersing the sample into the hot water.