Introduction to Superconductivity

Physicists before the 20th century observed that in a simple circuit with just a battery, light bulb, and a conducting wire (like the one shown above), the light bulb was dimmer at high temperatures and brighter at low temperatures. This is due to the fact that a wire’s resistance is proportional to the temperature. At high temperatures, the particles contained inside the wire would bump into each other more frequently which contributes to a greater energy loss and hence resulting in higher resistance. The strength of the current is what determines the brightness and from Ohm’s Law [V = I*R] (where V is voltage or potential difference, I = current, R = resistance), holding V constant, if R decreases, I increases.

At the time scientists did not have the technology necessary to observe what would happen to the resistance at very low temperatures near absolute zero. In the 20th century however, much to everybody’s surprise, it was observed that the resistance fell to zero below a certain temperature (this is called the critical temperature) for some materials. Materials that are in this state are called superconductors. In a superconductor, due to the absence of resistance, once current is generated, it will continue to flow eternally even without a power supply (e.g. battery). Superconductors are used in Maglev trains, MRI scanners, particle accelerators…etc.