Carbonaceous sulfur hydride

Prior to 1911, all known electrical conductors exhibited electrical resistance, due to collisions of the charge carrier with atoms in the material. Researchers discovered that in certain materials at low temperatures, the charge carriers interact with phonons in the material and form Cooper pairs, as described by BCS theory. This process results in the formation of a superconductor, with zero electrical resistance. During the transition to the superconducting state, the magnetic field lines are expelled from the interior of the material, which allows for the possibility of magnetic levitation. The effect has historically been known to occur at only low temperatures, but researchers have spent decades attempting to find a material that could operate at room temperature.[5]

The material is a ternary polyhydride compound of carbon, sulfur and hydrogen with a chemical formula that is thought to be CSH₈. As of October 2020, the material's molecular structure remains uncharacterized, as extreme pressures and the light elements used are unsuitable for most measurements, such as X-ray determination.[3] The material is synthesized by compressing methane (CH₄), hydrogen sulfide (H₂S) and hydrogen (H₂) in a diamond anvil cell and illuminating with a 532 nm green laser.[3] A starting compound of carbon and sulfur is synthesized with a 1:1 molar ratio, formed into balls less than five microns in diameter, and placed into a diamond anvil cell. Hydrogen gas is then added and the system is compressed to 4.0 GPa and illuminated with a 532-nm laser for several hours. It was reported that the crystal is not stable under 10 GPa and can be destroyed if left at room temperature overnight.[3] Research into the material is ongoing and, as of August 2020, scientists have yet to determine its molecular structure.[2]

On 14 October 2020, it was reported that carbonaceous sulfur hydride had been confirmed as the world's first room-temperature superconductor.[2][6][7][8][9][5][10] The superconducting state was observed at temperatures as high as 15 °C (59 °F).[11][12] The material sets a new record for high-temperature superconductivity, with a transition temperature almost 30 °C (54 °F) higher than the previous record holder.[4] With a high superconducting transition of 15 °C, it is the first material known which does not have to be cooled to enter a superconducting phase.[2] Despite the enormous advancement, the superconducting state is observable only at the very high pressure of 267 GPa (38.7 million psi), which is about a million times higher than the pressure in a typical car tyre.[12]

The discovery was published in Nature by a team of scientists led by Ranga Dias from the University of Rochester.[2][3] The article published results from several different experiments using the same material. The highest superconducting transition temperature found was 287.7 ± 1.2 K (14.6 ± 1.2 °C; 58.2 ± 2.2 °F) at a pressure of 267 ± 10 GPa (38.7 ± 1.5 million psi). The material was tested at several lower pressures, finding that at 138 ± 7 GPa (20.0 ± 1.0 million psi), the transition temperature is lowered to 147 K (−126 °C; −195 °F).[3] In addition, as expected from BCS theory, a notable decrease in the transition temperature was found when an external magnetic field is applied. The scientists found that the transition temperature was lowered by 22 K (40 °F) in a nine-tesla magnetic field at a pressure of 267 GPa.[3]

The validity of these results has been called into question in arXiv:2010.10307 and arXiv:2012.10771.