Superconductors Superconductors all in a Spin
27 Apr 2010




The phenomenon of superconductivity was discovered less than one hundred years ago, in 1911.

A magnet floating above a superconductor due to the Meissner Effect

The discovery was made by H. Kamerlingh Onnes following his success in liquefying the gas helium.  Using liquid helium Onnes was able to reach temperatures that were only a few kelvin above absolute zero.

He found that the electrical resistance of various metals, such as lead and tin, completely disappeared once they had been cooled below a characteristic temperature for that material.  This is called the superconducting transition temperature.

The next big discovery in superconductivity came in 1933, when Meissner and Ochenfeld found that if a superconducting material is placed in a magnetic field and cooled through its superconducting transition temperature, it expels the magnetic field from its interior.

This is a very unusual magnetic property and shows that something more fundamental than the total loss of resistance happens to a material when it becomes a superconductor.

It was not until almost fifty years later that theoretical physics was able to describe why these metals become superconductors at low temperatures.

In 1957 three Americans, John Bardeen, Leon Cooper and Robert Schrieffer showed that it was the vibrations of the atoms in the structure of the metal that were responsible for superconductivity.  At very low temperatures these vibrations change the way that the electrons behave.  They allow the electrons to form loosely associated pairs which are able to move through the material without resistance.

In 1972 they were awarded the Nobel Prize for Physics 'for their jointly developed theory of superconductivity, usually called the BCS-theory'.