Carbonaceous sulfur hydride
Carbonaceous sulfur hydride is a room-temperature superconductor that was announced in October 2020. The material has a maximal superconducting transition temperature of at a pressure of 267 gigapascals (GPa). This is a pressure equivalent to three quarters of the pressure at the center of the Earth. The material is an uncharacterized ternary polyhydride compound of carbon, sulfur and hydrogen with a chemical formula that is thought to be CSH. Measurements under extreme pressure are difficult, and in particular the elements are too light for an X-ray determination of crystal structure (X-ray crystallography). This is  the closest to room temperature achieved for a superconductor, with an onset almost 30 °C higher than that of the previous record-holder. Background. 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. Synthesis. The material is a ternary polyhydride compound of carbon, sulfur and hydrogen with a chemical formula that is thought to be CSH. 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. The material is synthesized by compressing  methane (CH), hydrogen sulfide (HS) and hydrogen (H) in a diamond anvil cell and illuminating with a 532 nm green laser. 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. Research into the material  is ongoing and, as of August 2020, scientists have yet to determine its molecular structure. Superconductivity. On 14 October 2020, it was reported that carbonaceous sulfur hydride had been confirmed as the world's first room-temperature superconductor. The superconducting state was observed at temperatures as high as . The material sets a new record for high-temperature superconductivity, with a transition temperature almost higher than the previous record holder. 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. Despite the enormous advancement , the superconducting state is observable only at the very high pressure of , which is about a million times higher than the pressure in a typical car tyre. The highest superconducting transition temperature found was at a pressure of . The material was tested at several lower pressures, finding that at , the transition temperature is lowered to . 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 in a nine-tesla magnetic field at a pressure of 267 GPa . Superconductivity for sulfur hydrides without carbon was first reported in 2015 The validity of these results has been called into question mainly by Jorge E. Hirsch as well as others and also the unavailability of the data which has prompted an editor's note on the original paper. The criticism focus on the measurements of AC susceptibility used to test the superconductivity as the more standard Meissner effect is too hard to observe at the scale of the experiments nevertheless this effect has been measured latter on sulfur hydrides without carbon by another team but those results have also been  called into question.