Critical current enhancement in NbN/AlN multilayers

Measurements are presented of the critical current density, J/sub c/, and parallel upper critical field, H/sub c/2/sub parallel/, for the refractory superconductor/insulator multilayer system NbN/AlN. A dramatic increase in J/sub c/, together with an increase of H/sub c/2/sub parallel/, is observed with decreasing NbN layer thickness. The J/sub c/ 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 J/sub c/ values was also accomplished in a novel structure by addition of copper layers within the superlattice