Nature http://dx.doi.org/10.1038/nature14964 (2015)

For 22 years, a mercury-based copper-oxide superconductor has held the highest transition-temperature record of 164 K, under pressure. We still do not understand the mechanism of superconductivity in the cuprates, or how to increase the transition temperature in these exotic superconductors. It is thus truly exciting that A. P. Drozdov and co-workers now report 203 K superconductivity in a sulfur hydride above 90 GPa. Moreover, the superconductivity seems to be conventional, mediated by electron–phonon coupling as described by Bardeen–Cooper–Schrieffer (BCS) theory.

With such a small sample trapped in a diamond anvil cell, it is difficult to ascertain the exact compound of interest here. Metallic hydrogen is a tantalizing possibility, but H3S is the more likely candidate. It is a good metal and has strong covalent bonding between H and S. Although hydrides are usually insulators, doping or gating could be a way to drive them to behave like metals at ambient pressure. As BCS superconductivity puts no upper limit on transition temperatures, who knows what the future will hold?