High Temperature Superconductors

Scientists uncover origin of high-temperature superconductivity in copper-oxide compoundHigh-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 temperatures of well-known superconductors (Boiling point of liquid nitrogen for comparison)
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:

  1. 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.
  2. 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.

 

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Ishan Pratap

Ishan is an Astro Physics Geek.

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