Josephson and Giaever

Great Britain, Norway, Canada

Brian Josephson (Great Britain, 1940-) and Ivar Giaever (Norway, 1929-) won the Nobel Prize in 1973 for their contributions linked to the tunnel effect in superconductors. When two superconductors are separated by a small piece of insulating material or by space, the Cooper pairs can “travel” through this barrier if it is thin enough, thanks to the tunnel effect. This effect is well known in metals and enabled the invention of Scanning Tunneling Microscopes.

Ivar Giaever was the first to have the idea of conducting this experiment in superconductors, while he was attending a class on superconductivity. He was able to conduct the experiment at the General Electric Research in Canada, in 1960. He was able to measure the “gap”, this energy of the superconducting condensate theoretically predicted by Bardeen, Cooper and Schrieffer a few years before.

After Brian Josephson studied Giaever’s experiments, he predicted during his PhD in Cambridge at only 22, that a supercurrent should appear in a tunnel barrier even when no electric field is applied ! Not only does this current called “Josephson current” exist while no electric field is applied, it also curiously depends in a sinusoidal manner on the difference between the superconducting wave phases on both sides of the barrier. He also predicted that when an electric field is continuously applied to this barrier, a new alternative effect appears. These predictions that have since been verified enabled the creation of SQUIDs, which are small ultrasensitive devices using these tunnel barriers and these Josephson currents to detect magnetic fields.