Field-induced superconductor-to-insulator transition in Josephson-junction ladders

Abstract

The superconductor-to-insulator transition is studied in a self-charging model for a ladder of Josephson junctions in the presence of an external magnetic field. Path integral Monte Carlo simulations of the equivalent $(1+1)$-dimensional classical model are used to study the phase diagram and critical behavior. In addition to a superconducting (vortex-free) phase, a vortex phase can also occur for an increasing magnetic field and small charging energy. It is found that an intervening insulating phase separates the superconducting from the vortex phases. Surprisingly, a finite-size scaling analysis shows that the field-induced superconducting-to-insulator transition is in the KT universality class, even though the external field breaks time-reversal symmetry.