Materials
The superconductors devices run on today
Ten conductors, every one of them in a machine somebody can look up. Each page carries the published transition temperature, what runs on it, where that is written down, and the thing about it that ends programs.
Grouped by what the conductor can be made into, because that is what decides whether two of them are alternatives at all. The fields they are used in are on Applications, and the words are defined in the glossary.
Every conductor, side by side
| Conductor | Tc | Form | Where it runs |
|---|---|---|---|
| NbTi | 9.2 K | wire | MRI magnets; the LHC main dipoles; ITER’s poloidal field coils |
| Nb₃Sn | 18.3 K | wire | ITER’s toroidal field coils; the HL-LHC 11 T dipoles; high-field NMR magnets |
| REBCO | 92 K | tape | High-field fusion magnets (the 20 T SPARC toroidal-field model coil, 2021); superconducting power cables |
| MgB₂ | 39 K | wire | Conduction-cooled MRI without a liquid-helium bath |
| Bi-2212 | 85 K | wire | Round-wire inserts for magnets above 25 T |
| Nb | 9.3 K | film | Transmon circuit wiring and resonators; accelerator RF cavities |
| Al | 1.2 K | film | The Josephson junctions in transmon qubits (Al/AlOx/Al) |
| TiN | 4.5 K | film | High-quality-factor superconducting resonators; kinetic-inductance detectors |
| NbN | 16 K | film | Superconducting nanowire single-photon detectors |
| NbTiN | 15 K | film | Single-photon detectors and high-kinetic-inductance resonators |
Published values. The source for each is on the conductor’s own page.
Wire
Drawn or reacted into a round strand, which is what lets a conductor be cabled, transposed and wound the way a magnet shop already works.
niobium-titanium·9.2 K
NbTiA ductile niobium-titanium alloy, and the only superconductor that can be drawn into wire on machinery a copper mill would recognize.
niobium-tin·18.3 K
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.
magnesium diboride·39 K
MgB₂Magnesium diboride: two cheap, light, abundant elements that turned out in 2001 to superconduct far warmer than any other simple compound.
bismuth strontium calcium copper oxide·85 K
Bi-2212The one high-temperature superconductor that can be made as a round, isotropic wire, and the reason it exists inside the strongest research magnets in the world.
Tape
A superconducting layer grown on a metal ribbon. It reaches operating points nothing else does, and it carries current in a plane, which every design above it has to answer for.
Film
Deposited on a wafer and patterned. These carry almost nothing by magnet standards and are chosen for their surfaces, their junctions and their speed.
niobium·9.3 K
NbElemental niobium, which has the highest transition temperature of any element at ambient pressure, and the material most superconducting circuits are wired in.
aluminum·1.2 K
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.
titanium nitride·4.5 K
TiNA hard, chemically stable nitride whose transition temperature can be tuned during deposition, used where a resonator has to be small and quiet.
niobium nitride·16 K
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.
niobium titanium nitride·15 K
NbTiNNiobium nitride with titanium substituted into it, traded for a lower and better-controlled kinetic inductance and a cleaner microwave surface.
Every transition temperature above is a published value with its source on the conductor’s own page. The hundred and fifteen years of record behind them is on Reference.