Ranga Dias must have stopped looking for his precious sample of metallic hydrogen that mysteriously disappeared in 2017 (blog coverage here). He is now part of a large team that has reported the discovery of a carbon-sulfur-hydrogen material capable of room-temperature superconductivity at 287K and 267GPa (Snider et al. DOI). The article makes clear the lesson has been learned that pure metallic hydrogen is a bridge too far as the authors write that other elements can be thrown where "the specific stoichiometry does not seem to be as critical as having a hydrogen-rich chemical environment".

This line of research had started in 2015 when hydrogen sulfide was found to superconduct at 203K at 90GPa (DOI). When pressurized, this ordinary gas becomes metallic when converted to elemental sulfur and higher sulfur hydrides. In 2019 researchers also came come up with lanthanum decahydride which superconducts at 250K at 150 GPa which gives a idea of the potential of this type of compounds.

In the new work elemental carbon and sulfur were mixed in a ball mill, transferred to a diamond anvil cell, flooded with hydrogen gas, exposed to 532-nm laser light and pressurized. But what is the material that eventually formed and is responsible for the superconductance? The laser light is expected to break up the sulfur bonds and initiate the formation of hydrogen sulfide. At 4 GPa a crystalline material forms consisting of hydrogen sulfide, methane and dihydrogen. At 37 GPa all Raman features have disappeared and superconductivity only sharply increases above 220 GPa. Sulfur hydrides do not get a mention. The authors acknowledge that it was not possible to find out more about the structure of the material at this pressure at the atomic level but they announced they are working on X-ray techniques.


2022 update: article retracted by Nature editors! Dias is planning his revenge! (link)