Critical current enhancement in NbN/AlN multilayers

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Abstract
Measurements are presented of the critical current density, Jc, and parallel upper critical field, Hc2∥, for the refractory superconductor/insulator multilayer system NbN/AlN. A dramatic increase in Jc, together with an increase of Hc2∥, is observed with decreasing NbN layer thickness. The Jc enhancement arises from flux pinning in the AlN or at the NbN‐AlN interface, not at defects in the NbN structure. The results indicate that the development of superconductor/insulator composites is a viable strategy to increase the critical current. Thermal stabilization which does not degrade the very high Jc values was also accomplished in a novel structure by addition of copper layers within the superlattice.