We review experiments on small-capacitance Josephson junctions. When the Josephson junction is fabricated in the configuration of dc superconducting quantum interference device (SQUID), the Josephson coupling can be tuned IN SITU with an external magnetic field. The electrical transport properties of one-dimensional arrays of small-capacitance dc SQUIDs have been investigated in order to study the superconductor-insulator transition. The arrays have also been used to bias a single Josephson junction, and a clear Coulomb blockade of Cooper-pair tunneling has been observed in the single junction.
We report measurements on two-dimensional arrays of Josephson junctions with junction sizes down to 60 nm by 60nm. Due to their small size, these junctions belong to the class of mesoscopic systems: they show behavior which reveals the underlying quantum mechanical properties. Two energies characterize the junctions, the Josephson energy E (sub j) and the charging energy E (sub c). Arrays in which E (sub j) >> E (sub c) are superconducting around zero bias and at zero temperature, while arrays in which E (sub c) >> E (sub j), called charging arrays, are instead insulating. This is the basis of the superconductor-to-insulator (S-I) transition (Author)