Cotunneling Transport and Quantum Phase Transitions in Coupled Josephson-Junction Chains with Charge Frustration

TL;DR

This paper studies quantum phase transitions in coupled Josephson-junction chains influenced by charge frustration, highlighting cotunneling effects and their role in driving phase changes in the system.

Contribution

It reveals how cotunneling induces quantum phase transitions in coupled Josephson chains with charge frustration, especially near maximal frustration.

Findings

Cotunneling significantly affects transport properties.

Quantum phase transition occurs as Josephson coupling increases.

Universality class remains consistent near the symmetry line.

Abstract

We investigate the quantum phase transitions in two capacitively coupled chains of ultra-small Josephson-junctions, with emphasis on the external charge effects. The particle-hole symmetry of the system is broken by the gate voltage applied to each superconducting island, and the resulting induced charge introduces frustration to the system. Near the maximal-frustration line, where the system is transformed into a spin-1/2 Heisenberg antiferromagnetic chain, cotunneling of the particles along the two chains is shown to play a major role in the transport and to drive a quantum phase transition out of the charge-density wave insulator, as the Josephson-coupling energy is increased. We also argue briefly that slightly off the symmetry line, the universality class of the transition remains the same as that right on the line, still being driven by the particle-hole pairs.