Superconducting Hydrogen Sulfide.

The recent discovery of superconductivity above 200 K in hydrogen sulfide under high pressure marks a milestone in superconductor research. Not only does its critical temperature Tc exceed the previous record in cuprates by more than 50 K, the superconductivity in hydrogen sulfide also exhibits convincing evidence that it is of conventional phonon-mediated type. Moreover, this is the first time that a previously unknown high-Tc superconductor is predicted by theory and afterwards verified by experiment. In this Minireview, we survey the progress made in the last three years in understanding this novel material, and discuss unsolved problems and possible developments to encourage future investigations.