Andreev tunneling into a one-dimensional Josephson junction array

TL;DR

This paper investigates how Andreev tunneling behaves in a one-dimensional Josephson junction array near a superconductor-insulator transition, revealing non-linear conductance scaling and threshold effects related to the phase transition.

Contribution

It introduces a detailed analysis of Andreev tunneling in a 1D Josephson array with finite-range Coulomb interactions, highlighting the transition's impact on conductance behavior.

Findings

Non-linear conductance exhibits scaling near the transition.

In the superconducting phase, I-V curves follow a power-law.

In the insulating phase, Andreev current is blocked at a threshold.

Abstract

In this letter we consider Andreev tunneling between a normal metal and a one dimensional Josephson junction array with finite-range Coulomb energy. The $I-V$ characteristics strongly deviate from the classical linear Andreev current. We show that the non linear conductance possesses interesting scaling behavior when the chain undergoes a T=0 superconductor-insulator transition of Kosterlitz-Thouless-Berezinskii type. When the chain has quasi-long range order, the low lying excitation are gapless and the $I-V$ curves are power-law (the linear relation is recovered when charging energy can be disregarded). When the chain is in the insulating phase the Andreev current is blocked at a threshold which is proportional to the inverse correlation length in the chain (much lower than the Coulomb gap) and which vanishes at the transition point.