Superconductors: Super Cold and Super Cool
When electricity passes through a material, like the wire of a circuit, some of its energy is lost to heat and sound as the material resists the current. But what if a material didn’t have any resistance at all, so electricity could zoom through without losing a single bit?
That’s the basic principle of superconductors: certain materials with no resistance, so electricity passes through them with maximum efficiency. If you passed a current through a ring of ordinary metal, the current would lose energy and rapidly decay, but if you passed it through a ring of superconductive metal, the current could continue to loop around for over a billion years.
But there’s a catch—H. Kammerlingh Onnes, the guy who discovered superconductors, realised in 1911 that mercury only displayed superconductive properties when it was cooled to extremely low temperatures. When I say extremely low, I mean extreme. The first superconductors discovered had to be cooled to -270 degrees Celsius, which is just 3 degrees away from absolute zero, the lowest temperature anything can ever get. The temperature at which the superconductor’s resistivity drops to zero is called its critical temperature.
Then, in 1986, researchers in Switzerland discovered a new class of superconductors, based on ceramic materials, that have superconductive properties at just -200 degrees Celsius. These types of material have received a lot of attention, because you only need liquid nitrogen to cool them down, which is relatively cheap and accessible.
We currently know of around thirty pure metals that have superconducting properties, and these are called Type I superconductors. They also exhibit an amazing magnetic property called the Meissner effect: they exclude magnetic fields from their interiors, meaning there is zero magnetic field inside a superconductor. Downside is, the magnetic fields are pretty small so their practicality is limited.
Type II superconductors, on the other hand, are made up of alloys—compounds of two or more materials like copper or lead. They have to be cooled to much lower temperatures than Type I before they exhibit superconducting properties, but it’s worth the effort because they have much higher and more stable magnetic fields. As a result, they’re exploited in magnetic levitation transport—maglev trains developed in Japan use superconducting magnetic coils, though the overall levitation isn’t due to the Meissner effect.
Using superconductors in everyday ways like electricity and transport isn’t yet possible, because the process of keeping superconductors cold uses up a bunch of energy—so even though no electricity is lost by the superconductor itself, they’re still not economical to use. Current superconductors are only utilised in niche areas, such as particle accelerators or magnets for nuclear spin tomography. Ongoing research is trying to develop materials that become superconductive at warmer temperatures, and one study has successfully used high-powered lasers to briefly create a room-temperature superconductor. When superconductors become efficient and accessible, the applications will be super cool.
