Insulating State of a Quasi-1-Dimensional Superconductor

TL;DR

This paper experimentally demonstrates that ultra-narrow quasi-1D superconducting nanowires exhibit Coulomb blockade due to quantum phase slips, leading to an insulating state, and confirms the duality with Josephson junctions.

Contribution

It provides experimental evidence of Coulomb blockade in superconducting nanowires, supporting the duality with Josephson junctions and revealing an insulating state induced by quantum phase slips.

Findings

Coulomb blockade observed in narrow superconducting nanowires.

The blockade disappears under magnetic field or above critical temperature.

The system acts as a dynamic chain of Josephson junctions.

Abstract

The topic of quantum fluctuations in quasi-1D superconductors, also called quantum phase slips (QPS), has attracted a significant attention. It has been shown that the phenomenon is capable to suppress zero resistivity of ultra-narrow superconducting nanowires at low temperatures T<<Tc and quench persistent currents in tiny nanorings. It has been predicted that a superconducting nanowire in the regime of QPS is dual to a Josephson junction. In particular case of an extremely narrow superconducting nanowire embedded in high-impedance environment the duality leads to an intuitively controversial result: the superconductor enters an insulating state. Here we experimentally demonstrate that the I-V characteristic of such a wire indeed shows Coulomb blockade, which disappears with application of critical magnetic field and/or above the critical temperature proving that the effect is related to superconductivity. The system can be considered as the dynamic equivalent of a chain of conventional Josephson junctions.