The search for the pairing symmetry in the high temperature superconductors

In his Nobel lecture in 1973, Ivar Giaever quoted from his laboratory notebook of May 2, 1960, as follows: “Friday April 22, I performed the following experiment aimed at measuring the forbidden gap in a superconductor”1. The experiment was a success, and so began 50 years of a field of research, applications and technology that includes superconducting tunneling spectroscopy, the Josephson Effect, SQUIDS, biomagnetism, low field MRI, far infrared detectors, quantum computing and single flux quantum logic. The work began somewhat earlier: after Esaki’s demonstration of electron tunneling in semiconductor diodes, Fisher and Giaever at General Electric began a program to see if tunneling could be observed in a very different system, namely between two metals separated by a thin insulator. After some unsuccessful experiments with other insulators between FIGURE 3.1: The first observation of the energy gap of a superconductor as revealed in the current-voltage and conductance-voltage characteristics of an Al/AlOx/Pb tunnel junction, by Ivar Giaever.