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

TL;DR

This paper investigates quantum critical phenomena in Josephson junction ladder systems under magnetic fields, revealing complex phase transitions influenced by magnetic flux and coupling ratios, with implications for understanding topological and quantum phase behavior.

Contribution

It introduces a detailed model of Josephson junction ladders in magnetic fields, analyzing topological phase diagrams and critical behaviors, highlighting new quantum transition mechanisms.

Findings

Superconductor-insulator transition at f=1/2 depends on coupling ratios.

Presence of commensurate-incommensurate and depinning transitions.

Critical behavior aligns with the XY-Ising universality class.

Abstract

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.