Quantum critical phenomena in ladders of Josephson junctions in a magnetic field

A model of a ladder of Josephson junctions in a magnetic field is considered. The topological features of the zero-temperature phase diagram, as a function of charging energy and small deviations from commensurability of the vortex lattice, are strongly dependent on the field. In addition to superconductor-insulator transitions, commensurate-incommensurate transitions and depinning by quantum fluctuations of the vortex-lattice are also possible. the critical behavior of the superconductor-insulator transition at f = 1/2 is found to depend on the ratio between interchain and intrachain Josephson couplings and is in the universality of the classical XY-Ising model.