Saturday, 24 January 2015

The Discovery of Superconductivity


That was year 1911, when the Dutch physicist Heike Kamerlingh Onnes discovered superconductivity. He realized that if mercury is cooled to below 4.2 degrees Kelvin, or about minus 269 degrees the resistance of the metal became exactly zero. This means that the current flowing in the cooled metal does not meet any "obstacle" and flows freely without giving rise to decrease of voltage or heating.

We can think of the current as a river of electrons moving in to the conductor; in their motion these particles are partially obstructed by the atoms of the metal itself that, in this way, subtract part of the energy of the electrons dissipating it as heat.

After the discovery of the Dutch physicist, who for this took the Nobel prize in 1913, the phenomenon of superconductivity has been observed in many other metals, each with its own critical temperature, namely at below which the metal becomes superconducting, and with the its critical magnetic field; in fact, not only the temperature affects the superconducting state of the metal but also a particularly intense magnetic field which, being able to penetrate inside the superconductor, alters the state of the superconducting metal and brings it back to the normal conductor.

This theory is known as the BCS, the initials of the three scientists Bardeen, Cooper and Schrieffer who have formulated in 1957 and for which they were awarded the Nobel Prize in 1972.