What is superconductivity?

Who would have thought that conductivity could be a superhero. Just kidding! Superconductivity means that a conductor (something that conducts electricity) has zero resistance. What does that mean? Well, the old familiar equation is E=I x R or volts equals current times resistance. If you rearrange this equation you see that I=E/R or current equals volts divided by resistance. If you have zero resistance you would end up with infinite current. Wow! That's awesome!

Unfortunately, it's not easy to accomplish. For one thing, most superconductive materials have to be reduced in temperature to only a few degrees Kelvin in order for superconductivity to happen. This is what physicists call cryogenic temperatures and it requires using liquid helium at 4.2 K or -269 C. The first example of superconductivity happened as far back as 1911, but it took until 1954 to actually make a practical superconductor, the cryotron, which is a switch that relies on the idea that magnetic fields suppress superconductivity. The cryotron uses a coil of tantalum and niobium wires immersed in liquid helium to create a superconductive switching device. Niobium wire in superconductivity mode has no resistance to current. However, the tantalum wire produced a magnetic field that inhibits the superconductivity of the Niobium, thus acting as a gate to control electrical conductivity through the switch.

The first commercial superconductor was a niobium-titanium alloy. Westinghouse scientists used this to make a superconducting magnet. Superconductive wires in an electromagnet can produce strong magnetic power, allowing heavy objects to be levitated.

The holy grail of superconductivity is to make it work at higher temperatures and eventually room temperature. This trick involves some very complicated material science. The first step was to replace liquid helium (4K) with liquid nitrogen (which is cheaper and at 77K). This was accomplished with (YBCO) Yttrium barium copper oxide. There's a mouth full! This stuff made it possible to produce superconductivity at 92 K. That's virtually warm compared to liquid helium.

So far, the highest superconductivity temperature obtained is around 138 K with the use of a substance that contains mercury, barium, calcium, copper and oxygen. Even that is a long way from room temperature (~ 295 K).

Scientists at the Institute of Physics, Chinese Academy of Sciences found that when they increased the pressure on a iron selenide crystal superconductor, they were able to increase its superconducting temperature from 30 K to 48 K. Iron selenide is a common superconductor material and this research could lead to a better understanding of how it works.

There have been several reports of room temperature superconductors. None of them have been verified. These include oxygen doped diamond; palladium hydride; graphite treated with pure water; YBCO when radiated with infrared laser pulses.

What good is superconductivity? Mostly, it's used to make powerful magnets that can be used in colliders and mass spectrometers. However, one use would be to create a powerful ion drive engine for spaceships. Something like that could be the ticket to another solar system where life could be found.

Thanks for reading.