Superconductivity was first discovered by Dutchman and physicist Heike Kamerlingh Onnes, when Liquid Mercury was cooled to just 4.2 Kelvins!! (Using some very
expensive Liquid Helium) While measuring the resistance of the substance, Onnes found that at this specific temperature, the resistivity of the substance quite literally dropped down to nothing. Zero Ohms.
But whats the significance?
Firstly, Onnes had discovered a material that would produce no heat when an electrical current flowed through it, which has huge technical implications.
It is being discussed, for instance, whether superconductors can be used to levitate trains (the Japanese are researching a system called MagLev) or transmit power more effectively. Lesser known applications include more effective Magnetic Resonance Imaging (MRI's), more detailed SQUIDS (magnetic field sensors with a variety of applications, namely detecting brain activity), or even to shrink computers down by using smaller wires!
What's more, a fascinating phenomenon coined the Meissner Effect goes into action whenever a magnet approaches the superconductor.
[ATTACH=CONFIG]127[/ATTACH]The superconductor literally "mirrors" the approaching magnet. For example, if a north pole approaches the material, an identical north pole will be created in the superconductor, allowing the magnet to levitate at a careful height.
A more detailed description of this effect derives from essential Electromagnetic concepts, namely the popular Lenz's Law.
In a conductor, free moving electrons are always present. When a changing electric field is introduced to a conductor, these electrons seek to flow such that they perfectly cancel any changing field strengths. Unfortunately for the electrons, a great deal of resistance is present in most conductors, which prevents the flow of the electrons from canceling the change in magnetic flux. Thus, we become familiarized with a Lenz's law that provides usually only minimal resistance to flux change.
Now the crazy physics begins. In a superconductor, a substance that has negligible resistance, these electrons are able to flow in such a manner that the changing magnetic field is completely canceled! Result: Floating magnets. Whats more, is that the magnetic field doesn't need to be changing for the Meissner effect to go into action! For this reason, the Meissner effect is different than normal diamagnetism (a term that refers to conductors that follow Lenz's Law).
Holy Floating Magnets, Batman! This is an example of a sample cooled with liquid nitrogen, with a cubical magnet suspended above the superconductive material. You may have noticed the thin layer of mist above the conductor; this mist is actually condensed oxygen! This oxygen jumps up to the magnet when it gets too close and quickly evaporates. This is because oxygen becomes liquid at warmer temperatures than liquid nitrogen, and also because oxygen is naturally "paramagnetic" meaning its molecules are attracted to magnetic fields a just a little bit more powerfully than other elements.
Superconductors, however, have a long way to go before they become reasonable. Numerous limitations exist. The hottest a superconductor has ever been is 138 Kelvin. The greatest challenge scientists face is getting the near perfect conditions of the laboratory into a household setting. But the future is coming! Its coming fast.