Maximum screening fields of superconducting multilayer structures

TL;DR

This paper demonstrates that multilayer superconducting structures can surpass the superheating magnetic field limits of individual layers, enabling higher magnetic fields and improved cavity performance.

Contribution

It introduces a method to optimize multilayer superconducting structures for enhanced magnetic screening beyond traditional superheating fields.

Findings

Multilayers can fully screen magnetic fields exceeding individual layer superheating fields.

Optimized multilayers could double the rf breakdown field in superconducting cavities.

A thin dirty Nb layer can increase the superheating field from 240 mT to 290 mT.

Abstract

It is shown that a multilayer comprised of alternating thin superconducting and insulating layers on a thick substrate can fully screen the applied magnetic field exceeding the superheating fields $H_s$ of both the superconducting layers and the substrate, the maximum Meissner field is achieved at an optimum multilayer thickness. For instance, a dirty layer of thickness $\sim 0.1\; \mu$m at the Nb surface could increase $H_s\simeq 240$ mT of a clean Nb up to $H_s\simeq 290$ mT. Optimized multilayers of Nb$_3$Sn, NbN, some of the iron pnictides, or alloyed Nb deposited onto the surface of the Nb resonator cavities could potentially double the rf breakdown field, pushing the peak accelerating electric fields above 100 MV/m while protecting the cavity from dendritic thermomagnetic avalanches caused by local penetration of vortices.