Coherent Flux Tunneling Through NbN Nanowires

TL;DR

This paper presents experimental evidence of coherent magnetic flux tunneling in NbN superconducting nanowires, demonstrating flux superposition in metallic superconducting loops and comparing results with theoretical models.

Contribution

First demonstration of flux tunneling in NbN nanowires, extending the phenomenon previously observed in InOx to a fully metallic superconductor.

Findings

Flux superposition observed in NbN loops

Tunneling amplitude varies with wire width

Experimental results align with theoretical models

Abstract

We demonstrate evidence of coherent magnetic flux tunneling through superconducting nanowires patterned in a thin highly disordered NbN film. The phenomenon is revealed as a superposition of flux states in a fully metallic superconducting loop with the nanowire acting as an effective tunnel barrier for the magnetic flux, and reproducibly observed in different wires. The flux superposition achieved in the fully metallic NbN rings proves the universality of the phenomenon previously reported for InOx. We perform microwave spectroscopy and study the tunneling amplitude as a function of the wire width, compare the experimental results with theories, and estimate the parameters for existing theoretical models.