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

TL;DR

This paper investigates the superconductor-insulator transition in Josephson-junction ladders under magnetic fields, revealing a vortex phase and a transition in the KT universality class despite broken time-reversal symmetry.

Contribution

It introduces a detailed phase diagram and critical behavior analysis of the field-induced transition in Josephson-junction ladders using Monte Carlo simulations.

Findings

Identification of a vortex phase at high magnetic fields

Discovery of an intervening insulating phase

Transition belongs to the KT universality class despite broken symmetry

Abstract

The superconductor to insulator transition is studied in a self-charging model for a ladder of Josephson-junctions in 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 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 tough the external field breaks time-reversal symmetry.