High-temperature superconductors (abbreviated high-Tc or HTS) are materials that have a superconducting transition temperature (Tc) above 30 K, which was thought (1960-1980) to be the highest theoretically allowed Tc. The first high-Tc superconductor was discovered in 1986 by Karl Müller and Johannes Bednorz, for which they were awarded the Nobel Prize in Physics in 1987. The term high-temperature superconductor was used interchangeably with cuprate superconductor until Fe-based superconductors were discovered in 2008. The best known high-temperature superconductors are bismuth strontium calcium copper oxide, BSCCO and yttrium barium copper oxide, YBCO.In 2015, hydrogen sulfide (H2S) under extremely high pressure was found to undergo superconducting transition near 203 K, the highest temperature superconductor known to date.
Examples:
| Transition temperature (in kelvin) |
Transition temperature (in Celsius) |
Material | Class |
|---|---|---|---|
| 203 | −70 | H2S (at 150 GPa pressure)[9] | Hydrogen-based superconductor |
| 195 | −78 | Sublimation point of dry ice | |
| 184 | −89.2 | Lowest temperature recorded on Earth | |
| 133 | −140 | HgBa2Ca2Cu3Ox(HBCCO) | Copper-oxide superconductors |
| 110 | −163 | Bi2Sr2Ca2Cu3O10(BSCCO) | |
| 93 | −180 | YBa2Cu3O7 (YBCO) | |
| 90 | −183 | Boiling point of liquid oxygen | |
| 77 | −196 | Boiling point of liquid nitrogen | |
| 55 | −218 | SmFeAs(O,F) | Iron-based superconductors |
| 41 | −232 | CeFeAs(O,F) | |
| 26 | −247 | LaFeAs(O,F) | |
| 20 | −253 | Boiling point of liquid hydrogen | |
| 18 | −255 | Nb3Sn | Metallic low-temperature superconductors |
| 10 | −263 | NbTi | |
| 9.2 | −263.8 | Nb | |
| 4.2 | −268.8 | Boiling point of liquid helium | |
| 4.2 | −268.8 | Hg (mercury) | Metallic low-temperature superconductors |
Properties:
“High-temperature” has two common definitions in the context of superconductivity:
- Above the temperature of 30 K that had historically been taken as the upper limit allowed by BCS theory(1957). This is also above the 1973 record of 23 K that had lasted until copper-oxide materials were discovered in 1986.
- Having a transition temperature that is a larger fraction of the Fermi temperature than for conventional superconductors such as elemental mercury or lead.This definition encompasses a wider variety of unconventional superconductors and is used in the context of theoretical models.
Applications:
low thermal loss current leads for LTS devices (low thermal conductivity)
RF and microwave filters (low resistance to RF)
increasingly in specialist scientific magnets, particularly where size and electricity consumption are critical while HTS wire is much more expensive than LTS in these applications, this can be offset by the relative cost and convenience of cooling); the ability to ramp field is desired or cryogen free operation is desired.
