Dichotomy in short superconducting nanowires: thermal phase slippage vs. Coulomb blockade

TL;DR

This study investigates ultrashort superconducting nanowires near the quantum transition, revealing a dichotomy where thermally activated phase slips dominate in the superconducting phase and Coulomb blockade effects govern the insulating phase, with no metallic intermediate.

Contribution

It provides experimental evidence distinguishing the true superconducting phase from the insulating phase in ultrashort nanowires, clarifying the nature of the quantum transition.

Findings

Superconducting phase explained by thermally activated phase slips.

Insulating phase behavior consistent with Coulomb blockade theories.

No evidence of an intermediate metallic phase.

Abstract

Quasi-one-dimensional superconductors or nanowires exhibit a transition into a nonsuperconducting regime, as their diameter shrinks. We present measurements on ultrashort nanowires (~40-190 nm long) in the vicinity of this quantum transition. Properties of all wires in the superconducting phase, even those close to the transition, can be explained in terms of thermally activated phase slips. The behavior of nanowires in the nonsuperconducting phase agrees with the theories of the Coulomb blockade of coherent transport through mesoscopic normal metal conductors. Thus it is concluded that the quantum transition occurs between two phases: a "true superconducting phase" and an "insulating phase". No intermediate, "metallic" phase was found.