Topological phase transition in 2D quantum Josephson array

TL;DR

This study uses Path Integral Quantum Monte Carlo simulations to analyze the phase diagram of a 2D quantum Josephson array, revealing a continuous Kosterlitz-Thouless transition driven by quantum fluctuations.

Contribution

It provides the first detailed analysis of the quantum phase transition in a 2D Josephson array using Monte Carlo methods, identifying the transition as of Kosterlitz-Thouless type.

Findings

No reentrant phase transition observed in the q-T plane.

The phase transition line is of Kosterlitz-Thouless type.

Quantum fluctuations induce a superconductor-normal phase transition.

Abstract

Path Integral Quantum Monte Carlo simulation is used to study thermodynamic properties and a phase diagram of 2D quantum Josephson array, described by 2+1 XY model. The helicity and vorticity moduli, correlation function of phases and other characteristics of the system as functions of quantum parameter $q$ and temperature $T$ are studied ($q=2e/\sqrt{JC_0}$, $J$ is the Josephson coupling constant, $C_0$ is the intragrain capacitance). Quantum fluctuation induced superconductor - normal phase transition is studied in detail through the use of behavior of above-mentioned quantities. No discontinuous or reentrant phase transition in $q-T$ plane is found. Analysis of the vorticity and the renormalized coupling constant leads to the conclusion that the whole line of phase transition is of Kosterlitz - Thouless type.