Superconductor-insulator transition in Josephson junction chains by quantum Monte-Carlo

TL;DR

This paper investigates the zero-temperature phase diagram of a Josephson junction chain, identifying the critical Josephson energy for the superconductor-insulator transition using quantum Monte Carlo simulations.

Contribution

Develops an efficient quantum Monte Carlo algorithm in the charge representation to study the phase transition in Josephson junction chains, revealing the importance of anharmonic effects.

Findings

Critical Josephson energy depends on capacitance ratios.

Anharmonic corrections significantly influence the phase diagram.

Standard Kosterlitz-Thouless theory does not fully capture the transition.

Abstract

We study the zero-temperature phase diagram of a dissipationless and disorder-free Josephson junction chain. Namely, we determine the critical Josephson energy below which the chain becomes insulating, as a function of the ratio of two capacitances: the capacitance of each Josephson junction and the capacitance between each superconducting island and the ground. We develop an imaginary-time path integral Quantum Monte-Carlo algorithm in the charge representation, which enables us to efficiently handle the electrostatic part of the chain Hamiltonian. We find that a large part of the phase diagram is determined by anharmonic corrections which are not captured by the standard Kosterlitz-Thouless renormalization group description of the transition.