Andreev tunneling into a one-dimensional Josephson junction array

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.