Capacitively coupled Josephson-junction chains: straight and slanted coupling

TL;DR

This paper investigates how capacitive coupling in Josephson-junction chains influences quantum phase transitions, revealing that increased coupling induces an insulator-to-superfluid transition with distinct mechanisms for straight and slanted coupling schemes.

Contribution

It introduces and analyzes two coupling schemes in Josephson-junction chains, demonstrating their impact on quantum phase transitions and identifying differences in transition points.

Findings

Transport of particle-hole pairs drives the transition.

Transition belongs to the Berezinskii-Kosterlitz-Thouless class.

Different coupling schemes have distinct transition points.

Abstract

Two chains of ultrasmall Josephson junctions, coupled capacitively with each other in the two different ways, straight and slanted coupling, are considered. As the coupling capacitance increases, regardless of the coupling scheme, the transport of particle-hole pairs in the system is found to drive the quantum-phase transition at zero temperature, which is a insulator-to-superfluid transition of the particle-hole pairs and belongs to the Berezinskii-Kosterlitz-Thouless universal class. The different underlying transport mechanisms for the two coupling schemes are reflected in the difference between the transition points.