Magnetic Field Characteristics of Multiple Niobium Three-dimensional Nano-bridge Junctions in Parallel

Abstract

The superconducting device of multiple Josephson junctions in arrays has increasingly attracted interest in both applications and fundamental research. The challenge of array integration and scaling is a wide concern. The present study investigated superconducting devices of multiple niobium three-dimensional nano-bridge junctions (3D-NBJs) in parallel. We fabricated evenly and unevenly spaced devices of three to six 3D-NBJs in parallel. We measured the critical current as a function of the magnetic field and voltage to magnetic field transfer function of each device. The derivative of voltage with respect to the magnetic field at the sensitive point increased linearly with the number of junctions. A maximal derivative of 97.3 V/T was achieved by our device with six unevenly spaced junctions in parallel. Furthermore, we carried out numerical simulations on devices of three and four junctions in parallel using the current–phase relation of a single 3D-NBJ. The CPR was determined by comparing the measured and simulated magnetic flux modulations of nano-SQUID. Qualitative agreement between the numerical simulation and experimental measurement suggests that it is possible to use 3D-NBJs to build SQUID arrays or SQIFs with high integration density.