Observation of Josephson Effec

q First reported observation of the DC Josephson effect and its magnetic field dependence 1 Discovery of the AC Josephson effect 1 First verification of the frequency-voltage relation of the AC Josephson effect f Discovery that the established fine structure constant α, although theoretically supported, was wrong. The hyper-fine structure α was right. This reversal, based on an imaginative application of the Josephson effect, removed the discrepancy between the theoretical and experimental values of the hyperfine splitting in the ground state of hydrogen-one of the major unsolved problems of quantum electro-dynamics at that time (1966). The tunnel effect in semiconductors and insulators is a special case of the general quantum-mechanical phenomenon of the passage of particles through potential barriers. Classically, a particle can never cross a region of space where there is a potential barrier whose height V. exceeds the particle's total energy E, because its kinetic energy inside the barrier would be negative. However , when the wave aspect of the particle is taken into consideration, there exist, in the barrier, solutions of Schrodinger's equation which decay exponentially with depth of penetration. The particle has thus a finite probability of being found on the far side of the barrier, as if it had 'tunneled' through the potential mountain. Probably the best known case of tunnel effect is the passage of apart -icles through the potential barrier surrounding atomic nuclei. But the effect occurs very widely: for instance, in nuclear reactions, in many molecular phenomena, in field emissions from metals, etc. In semiconductors and insulators, one means by 'tunnel effect' the internal field emission first considered by Zener in 1934 to explain dielectric breakdown in dielectrics (though it is now known that ordinary breakdown occurs generally through different mechanisms). For an electron in an insulator, the gap between the conduction band and the valence band behaves as a potential barrier. The width of the barrier is determined by the magnitude of the field. There is thus a finite probability for the electron, without changing its energy, to tunnel across the forbidden gap into the empty conduction band. This process creates an electron-hole pair. As this chapter was being prepared for publication, the 1973 Nobel Prize for Physics was announced. The award is relevant to the subject of this chapter, as it was shared by three physicists for their work on tunneling effects. One half of the prize went to Brian …