PERSISTENT CURRENT AND VOLTAGE IN A RING OF JOSEPHSON-JUNCTIONS

We study a ring of N Josephson junctions with gauge charges induced by external sources and in the presence of a magnetic field. At zero temperature the system is mapped into a standard two-dimensional classical XY model, thus shown to exhibit the Kosterlitz-Thouless transition between the superconducting and the insulating phases, which are characterized by the gauge-invariant phase and charge correlation functions. In particular, the persistent current and voltage in the two phases are obtained, and the duality relation between the strong-coupling limit and the weak-coupling limit is discussed.