Fundamentals of Giaever and Josephson Tunneling

Abstract

The concept of quantum-mechanical tunneling of a particle through a potential barrier has been applied successfully to explain various phenomena occurring in physics and chemistry. We introduce two very recent and exciting applications of electron tunneling: the scanning tunneling microscope (STM) and single-electron effects in very small junctions. Next, we focus on the tunneling of electrons between superconducting electrodes separated by a potential barrier. The current-voltage characteristics of hysteretic (superconductor-oxide-superconductor) as well as non-hysteretic junctions (weak links between two superconductors) are discussed in detail. The importance of Giaever (quasiparticle) tunneling and Josephson (Cooper pair) tunneling is clearly emphasized. After deriving the fundamental relations for the dc and ac Josephson effect, we consider the pronounced influence of a magnetic field. For a loop containing two Josephson junctions in parallel, the magnetic flux quantization gives rise to the dc SQUID (Superconducting QUantum Interference Device) effect, which can now be observed for weak links in thin films of high-T c material.