John Bardeen (United States, 1908-1991), Leon Cooper (United States, 1930-) and Robert Schrieffer (United States, 1931-) won the Nobel Prize in 1972 because they understood superconductivity in metals and alloys and gave their initials to the theory they discovered in 1957, the BCS theory. John Bardeen had already won the Nobel Prize thanks to his discovery along with Brattain and Shockley of the transistor effect, which revolutionized modern electronics.
In 1955, Leon Cooper joined Bardeen and his PhD student Schrieffer. The three physicists tackled the problem: how can superconductivity be explained? They started to look for a model to explain how the electrons merge into a collective wavelength with, in addition to that, a “gap” in its energy spectrum. It was Cooper who took the first significant step when he showed that electrons could pair at low temperatures, forming what has since been called a “Cooper pair”. The three physicists were then able to extend the theory and were able to describe the collective wavefunction formed by these pairs and also predict its behaviour. They published the article “theory of superconductivity” in 1957 in “Physical Review”, and it has been the reference ever since. Not only did their theory enable to prove all the experimental results found in the 40 previous years, it also predicted new original behaviours. For instance the relaxation rate NMR increases before it drops when the material becomes superconducting: this strange result was observed shortly after by Charles Slichter. They won the Nobel Prize in 1972 for their theory and Bardeen became the only physicist to win the Nobel Prize in physics twice!
The BCS theory has been confirmed for more than 50 years in most superconductors, from metals to alloys. However, it seems to partly fail as far as new superconductors are concerned, but this does not question its validity in other materials. Today, we are waiting for the new Bardeen, Cooper and Schrieffer to explain these new superconductors.
