The basics
Critical temperature (Tc)
The temperature a material has to be colder than before it superconducts. It is the number the field has chased for a century, and it is quoted in kelvin.
Why critical temperature matters
A device team reads it as a refrigeration bill: above 77 K the coolant is liquid nitrogen, and below about 20 K it is liquid helium or a closed-cycle machine.
Where critical temperature comes up
Critical temperature in a real conductor
- Nb₃SnA brittle intermetallic with roughly twice the transition temperature of NbTi, and a manufacturing process built entirely around the fact that it cannot be bent.
- MgB₂Magnesium diboride: two cheap, light, abundant elements that turned out in 2001 to superconduct far warmer than any other simple compound.
- NbElemental niobium, which has the highest transition temperature of any element at ambient pressure, and the material most superconducting circuits are wired in.
- AlAluminum superconducts at close to the lowest useful temperature on this list, and nearly every superconducting qubit in the world is built from it anyway.
- TiNA hard, chemically stable nitride whose transition temperature can be tuned during deposition, used where a resonator has to be small and quiet.
- NbNA thin film with a high transition temperature for its class and a very short recovery time, which is what a single-photon detector is actually built around.
- NbTiNNiobium nitride with titanium substituted into it, traded for a lower and better-controlled kinetic inductance and a cleaner microwave surface.
Related to critical temperature
SuperMatics is a platform infrastructure company for superconducting devices: software that finds the material and the process, lab work that makes and measures it, and pilot manufacturing with industrial partners.If you have a device and a constraint it has to meet, tell us about it.