The work that led to Giaever's Nobel Prize was performed at General Electric in 1960. Following on Esaki's discovery of electron tunnelling in semiconductors in 1958, Giaever showed that tunnelling also took place in superconductors, demonstrating tunnelling through a very thin layer of oxide surrounded on both sides by metal in a superconducting or normal state. Giaever's experiments demonstrated the existence of an Energy gap in superconductors, one of the most important predictions of the BCS theory of Superconductivity, which had been developed in 1957. Giaever's experimental demonstration of tunnelling in superconductors stimulated the theoretical Physicist Brian Josephson to work on the phenomenon, leading to his prediction of the Josephson effect in 1962. Esaki and Giaever shared half of the 1973 Nobel Prize, and Josephson received the other half.