Superconducting insulators and localization of Cooper pairs

TL;DR

This paper explores how quantum phase slips in superconducting nanowires can lead to localization of Cooper pairs, causing a transition from superconducting to insulating behavior, and reveals a superposition of states in the insulating regime.

Contribution

It introduces the concept of QPS-controlled localization of Cooper pairs in uniform nanowires, supported by both experimental and theoretical evidence, highlighting flux-charge duality effects.

Findings

Deep in the insulating state, nanowires show a superposition of superconductivity and Coulomb blockade.

Quantum tunneling of fluxons contributes to the weak Coulomb blockade of Cooper pairs.

The study demonstrates a fundamental flux-charge duality in superconducting nanowires.

Abstract

Rapid miniaturization of electronic devices and circuits demands profound understanding of fluctuation phenomena at the nanoscale. Superconducting nanowires -- serving as important building blocks for such devices -- may seriously suffer from fluctuations which tend to destroy long-range order and suppress superconductivity. In particular, quantum phase slips (QPS) proliferating at low temperatures may turn a quasi-one-dimensional superconductor into a resistor or an insulator. Here, we introduce a physical concept of QPS-controlled localization of Cooper pairs that may occur even in uniform nanowires without any dielectric barriers being a fundamental manifestation of the flux-charge duality in superconductors. We demonstrate -- both experimentally and theoretically -- that deep in the "insulating" state such nanowires actually exhibit non-trivial superposition of superconductivity and weak Coulomb blockade of Cooper pairs generated by quantum tunneling of magnetic fluxons across the wire.